Mickelson was born in San Diego, California, to parents Philip Mickelson (an airline pilot and former naval aviator) and Mary Mickelson (née Santos); he was raised there and in Scottsdale, Arizona. Mickelson is of Portuguese and Sicilian descent on his mother’s side. His maternal grandfather, Alfred Santos (also Mickelson’s middle name) was a caddie at Pebble Beach Golf Links and took Phil golfing as a child. Although otherwise right-handed, he played golf left-handed since he learned by watching his right-handed father swing, mirroring his style. Mickelson began golf under his father’s instruction before starting school. Phil Sr.’s work schedule as a commercial pilot allowed them to play together several times a week and young Phil honed his creative short game on an extensive practice area in their San Diego backyard. Mickelson graduated from the University of San Diego High School in 1988.

Mickelson attended Arizona State University in Tempe on a golf scholarship and became the face of amateur golf in the United States, capturing three NCAA individual championships and three Haskins Awards (1990, 1991, 1992) as the outstanding collegiate golfer. With three individual NCAA championships, he shares the record for most individual NCAA championships alongside Ben Crenshaw. Mickelson also led the Sun Devils to the NCAA team title in 1990. Over the course of his collegiate career, he won 16 tournaments.

Mickelson was the second collegiate golfer to earn first-team All-American honors all four years. In 1990, he also became the first with a left-handed swing to win the U.S. Amateur title, defeating high school teammate Manny Zerman 5 and 4 in the 36-hole final at Cherry Hills, south of Denver. Mickelson secured perhaps his greatest achievement as an amateur in January 1991, winning his first PGA Tour event, the Northern Telecom Open, in Tucson, making him one of the few golfers to win a PGA Tour event as an amateur in the history of the PGA Tour. At age 20, he was only the sixth amateur to win a tour event and the first in over five years after Scott Verplank at the Western Open in August 1985. Other players to accomplish this feat include Doug Sanders (1956 Canadian Open) and Gene Littler (1954 San Diego Open). With five holes remaining, Mickelson led by a stroke, but made a triple-bogey and was then three behind. The leaders ahead of him then stumbled, and he birdied 16 and 18 to win by a stroke. To date, it is the most recent win by an amateur at a PGA Tour event.

* As of 2020 season. Mickelson won as an amateur in 1991 and therefore did not receive any prize money.

That April, Mickelson was the low amateur at the Masters Tournament in Augusta, Georgia. With his two-year PGA Tour exemption from the Tucson win, he played in several tour events in 1992 while an amateur but failed to make a cut.

Mickelson graduated from ASU in June 1992 and quickly turned professional. He bypassed the tour’s qualifying process (Q-School) because of his 1991 win in Tucson, which earned him a two-year exemption. In 1992, Mickelson hired Jim “Bones” Mackay as his caddy. He won many PGA Tour tournaments during this period, including the Byron Nelson Golf Classic and the World Series of Golf in 1996, the AT&T Pebble Beach National Pro-Am in 1998, the Colonial National Invitation in 2000 and the Greater Hartford Open in 2001 and again in 2002.

He appeared as himself in a non-speaking role in the 1996 film Tin Cup, starring Kevin Costner.

Tiger Woods had a dramatic return to competitive play after a scandal-ridden 20-week absence; he was in close contention throughout for the lead and finished tied with Choi for 4th at −11. Mickelson and others showed exciting play over the weekend, and the 2010 Masters had strong television ratings in the United States, ranking third all-time to Woods’s historic wins in 1997 and 2001. Mickelson’s win left him second only to Woods in major championships among his competitive contemporaries, moving him ahead of Ernie Els, Vijay Singh and Pádraig Harrington, with three major championships each and each, like Mickelson, with dozens of worldwide wins.

His 2000 Buick Invitational win ended Tiger Woods’ streak of six consecutive victories on the PGA tour. After the win, Mickelson said, “I didn’t want to be the bad guy. I wasn’t trying to end the streak per se. I was just trying to win the golf tournament.”

Mickelson’s first major championship win came in his thirteenth year on the PGA Tour in 2004, when he secured victory in the Masters with an 18-foot (5.5 m) birdie putt on the final hole. Ernie Els was the runner-up at a stroke back; the two played in different pairs in the final round and had traded birdies and eagles on the back nine. In addition to getting the “majors monkey” off his back, Mickelson was now only the third golfer with a left-handed swing to win a major, the others being New Zealander Sir Bob Charles, who won The Open Championship in 1963, and Canadian Mike Weir, who won The Masters in 2003. (Like Mickelson, Weir is a right-hander who plays left-handed.) A fourth left-handed winner is natural southpaw Bubba Watson, the Masters champion in 2012 and 2014.

Prior to the Ryder Cup in 2004, Mickelson was dropped from his long-standing contract with Titleist/Acushnet Golf, after an incident when he left a voicemail message for a Callaway Golf executive. In it he praised their driver and golf ball, and thanked them for their help in getting some equipment for his brother. This memo was played to all of their salesmen, and eventually found its way back to Titleist. He was then let out of his multi-year deal with Titleist 16 months early, and signed on with Callaway Golf, his current equipment sponsor. He endured a great deal of ridicule and scrutiny from the press and fellow Ryder Cup members for his equipment change so close to the Ryder Cup matches. He faltered at the 2004 Ryder Cup with a 1–3–0 record, but refused to blame the sudden change in equipment or his practice methods for his performance.

In November 2004, Mickelson tallied his career-low for an 18-hole round: a 59 at the PGA Grand Slam of Golf at Poipu Bay Golf Course in Hawaii.

Mickelson also has shown other signs of appreciation. In 2007 after hearing the story of retired NFL player, Conrad Dobler, and his family on ESPN explaining their struggles to pay medical bills, Mickelson volunteered to pay tuition for Holli Dobler, Conrad Dobler’s daughter, at Miami University in Oxford, Ohio.

Frustrated with his driving accuracy, Mickelson made the decision in April 2007 to leave longtime swing coach, Rick Smith. He then began working with Butch Harmon, a former coach of Tiger Woods and Greg Norman. On May 13, Mickelson came from a stroke back on the final round to shoot a three-under 69 to win The Players Championship with an 11-under-par 277.

On September 3, 2007, Mickelson won the Deutsche Bank Championship, which is the second FedEx Cup playoff event. On the final day, he was paired with Tiger Woods, who ended up finishing two strokes behind Mickelson in a tie for second. It was the first time that Mickelson was able to beat Woods while the two stars were paired together on the final day of a tournament. The next day Mickelson announced that he would not be competing in the third FedEx Cup playoff event. The day before his withdrawal, Mickelson said during a television interview that PGA Tour Commissioner, Tim Finchem, had not responded to advice he had given him on undisclosed issues.

In 2008, Mickelson won the Crowne Plaza Invitational at Colonial with a −14, one shot ahead of Tim Clark and Rod Pampling. Mickelson shot a first-round 65 to start off the tournament at −5. He ended the day tied with Brett Wetterich, two shots behind leader, Johnson Wagner. Mickelson shot a second round 68, and the third round 65, overall, being −12 for the first three rounds. On the final hole, after an absolutely horrendous tee shot, he was in thick rough with trees in his way. Many players would have punched out, and taken their chances at making par from the fairway with a good wedge shot. Instead, he pulled out a high-lofted wedge and hit his approach shot over a tree, landing on the green where he one-putted for the win.

Mickelson was inducted into the National Italian American Sports Hall of Fame in 2008.

In September, Mickelson won The Tour Championship for the second time in his career. He entered the final round four strokes off the lead, but shot a final round 65 to win the event by three strokes over Tiger Woods. With the win, Mickelson finished the season second behind Woods in the 2009 FedEx Cup standings.

*The 2009 WGC-HSBC Champions was an unofficial PGA Tour event, therefore the win is considered unofficial on the PGA Tour. Co-sanctioned by the Asian Tour, Sunshine Tour and PGA Tour of Australasia

In 2010, Mickelson won the Masters Tournament on April 11 with a 16-under-par performance, giving him a three-stroke win over Lee Westwood. The win marked the third Masters victory for Mickelson and his fourth major championship overall. Critical to Mickelson’s win was a dramatic run in the third round on Saturday in which Mickelson, trailing leader Westwood by five strokes as he prepared his approach shot to the 13th green, proceeded to make eagle, then to hole-out for eagle from 141 yards at the next hole, the par 4 14th, then on the next, the par 5 15th, to miss eagle from 81 yards by mere inches. After tapping in for birdie at 15, Mickelson, at −12, led Westwood, at −11, who had bogeyed hole 12 and failed to capitalize on the par 5 13th, settling for par.

Although ranked second on the PGA Tour’s all-time money list of tournament prize money won, Mickelson earns far more from endorsements than from prize money. According to one estimate of 2011 earnings (comprising salary, winnings, bonuses, endorsements and appearances) Mickelson was then the second-highest paid athlete in the United States, earning an income of over $62 million, $53 million of which came from endorsements. Major companies which Mickelson currently endorses are KPMG, ExxonMobil (Mickelson and wife Amy started a teacher sponsorship fund with the company), Rolex, Workday, Inc., Callaway Golf and Mizzen+Main. He has been previously sponsored by Titleist, Bearing Point, Barclays, and Ford. After being diagnosed with psoriatic arthritis in 2010, Mickelson was treated with Enbrel and began endorsing the drug.

On May 30, 2014, The Wall Street Journal reported that the FBI and U.S. Securities and Exchange Commission (SEC) were investigating Mickelson and associates of his for insider trading in Clorox stock. Mickelson denied any wrongdoing, and the investigation found “no evidence” and concluded without any charges. On May 19, 2016, Mickelson was named as a relief defendant in another SEC complaint alleging insider trading but completely avoided criminal charges in a parallel case brought in the Federal District Court for the Southern District of New York. The action stems for trades in Dean Foods in 2012 in conjunction with confidential information provided by Thomas Davis, a former director of Dean Foods Company, who tipped his friend and “professional sports bettor” Billy Walters.

Prior to the 2015 Masters, Mickelson’s best finish in 2015 was a tie for 17th. At the Masters, Mickelson shot rounds of 70-68-67-69 to finish tied for second with Justin Rose, four shots behind champion Jordan Spieth. The second-place finish was Mickelson’s tenth such finish in a major, placing him second all time only to Jack Nicklaus in that regard.

After leaving Butch Harmon, Mickelson hired Andrew Getson of Grayhawk Golf Club in Scottsdale, Arizona, to serve as his new swing coach. The two worked together heavily in the 2015 offseason to get Mickelson’s swing back.

In 2015, Forbes estimated Mickelson’s annual income at $51 million.

The SEC did not allege that Walters actually told Mickelson of any material, nonpublic information about Dean Foods, and the SEC disgorged Mickelson of the $931,000 profit he had made from trading Dean Foods stock and had him pay prejudgment interest of $105,000. In 2017, Walters was convicted of making $40 million on Davis’s private information from 2008 to 2014 by a federal jury. At that time, it was also noted that Mickelson had “once owed nearly $2 million in gambling debts to” Walters. Walters’ lawyer said his client would appeal the 2017 verdict.

On March 4, 2018, Mickelson ended a winless drought that dated back to 2013, by capturing his third WGC championship at the WGC-Mexico Championship, with a final round score of 66 and a total score of −16. Mickelson birdied two of his last four holes and had a lengthy putt to win outright on the 72nd hole, but tied with Justin Thomas. He defeated Thomas on the first extra hole of a sudden-death playoff with a par. After Thomas had flown the green, Mickelson had a birdie to win the playoff which lipped out. Thomas however could not get up and down for par, meaning Mickelson claimed the championship. The win was Mickelson’s 43rd on the PGA Tour and his first since winning the 2013 Open Championship. He also became the oldest winner of a WGC event, at age 47.

On November 23, 2018, Mickelson won the pay-per-view event, Capital One’s The Match. This was a $9,000,000 winner-takes-all match against Tiger Woods at Shadow Creek Golf Course in Las Vegas. Mickelson needed four extra holes to beat Woods, which he did by holing a four-foot putt after Woods missed a seven-foot putt on the 22nd hole.

In December 2019, Mickelson announced via Twitter that “after turning down opportunities to go to the Middle East for many years” he would play in Saudi International golf tournament and would miss Waste Management Phoenix Open for the first time since 1989. However, his decision to visit and play in Saudi Arabia was criticized for getting lured by millions of dollars and ignoring the continuous human rights abuse in the nation. Mickelson reportedly played his Wednesday pro-am round in Saudi Arabia with some of the prominent figures behind a potential start up rival to the PGA and European Tours, the Premier Golf League. Mickelson went on to finish the February 2020 event tied for third. This was his first top 10 finish since his win in the 2019 AT&T Pebble Beach National Pro-Am.

Mickelson finished 3rd at the 2020 AT&T Pebble Beach Pro-Am and tied for 2nd in the WGC-FedEx St. Jude Invitational. Mickelson was the first player over 50 to finish in the top five of a World Golf Championship event. He was ultimately eliminated from the FedEx Cup Playoffs following The Northern Trust at TPC Boston in August 2020. One week later, Mickelson made his debut on the PGA Tour Champions. He won the Charles Schwab Series at Ozarks National in his first tournament after becoming eligible for PGA Tour Champions on his 50th birthday on June 16, 2020. He was the 20th player to win their debut tournament on tour. Mickelson’s 191 stroke total tied the PGA Tour Champions all-time record for a three-day event.

In October 2020, Mickelson won the Dominion Energy Charity Classic in Virginia. It was his second win in as many starts on the PGA Tour Champions.