Nicknamed by many as "Phil the Thrill," the American left-hander has long been one of the biggest drawcards in the game, capable of driving up television ratings almost single-handedly when in contention for one of the sport's bigger events.
For all of that, though, it is difficult to picture a bolder on-course statement made by Mickelson, or a more career-defining moment, than his astonishing final round of five-under-par 66 in last week's Open at Muirfield to triumph by three shots.
Not only did he clinch his fifth Major title in commanding fashion but he did so after scaling heights of near-perfection with his putter as he authored a brilliant display of links course golf, a format which has never come naturally to him.
Mickelson himself said he had never putted better, and that his closing 66 was "probably the best round of my career."
It certainly ranks among the greatest final rounds at a Major, given the difficult scoring conditions on a course running fast and firm with a top-quality leaderboard that was tightly bunched until Mickelson stormed ahead with four birdies in the last six holes.
Most golf fans would agree that the last-day 65 posted by Jack Nicklaus at the 1986 Masters, where he won his record 18th Major title aged 46, is unbeatable for its blend of brilliant shot-making, raw emotion, pulsating drama and perfect timing.
However, Mickelson's 66 compares favourably in quality with the 63 fired by Johnny Miller at the 1973 US Open, Tom Watson's 65 at the 1977 Open, Gary Player's 64 at the 1978 Masters and Greg Norman's 64 at the 1993 Open.
Nicklaus, who is as good a judge of quality as anyone else in the game, past or present, described Mickelson's 66 as "incredible" when he tweeted his congratulations shortly after Sunday's final round.
This week, the 73-year-old golfing great went on to say that his fellow American had cemented his place among the game's elite with the quality of his Muirfield triumph.
"Phil is going to go down in history as one of the great players of the game, there's no question about that," said Nicklaus. "There's no argument about Hall of Fame.
"His ability to see that he needed to adapt himself to the Scottish conditions was much to his credit. I give him great kudos for what he's done."
For Nicklaus, the brilliance of Mickelson was best exemplified by the way he played the last three holes in the final round, saving par at the short 16th after his ball rolled back off the green from the tee before finishing birdie-birdie.
"After his bad break on 16 and to then get up and down showed a lot of guts," said Nicklaus. "And the two great shots at 17 ended the tournament. I want to offer my sincere congratulations on a championship well played."
Mickelson's swing coach Butch Harmon, who has played a significant role in his pupil's increased comfort level in links course golf since they began working together in 2007, was blown away by the American's superb finish at a windy Muirfield.
"I said when Greg Norman won in 1993 that that was the best round of golf I'd seen, but I think this one tops it," Harmon told the BBC. "To go around when you knew you had to do it is absolutely brilliant.
"It took him a long time to understand how to play links golf. Phil plays very aggressive, but you can't do that with links golf. He just embraced how to play on links."
Prior to last week, Mickelson's status as one of the game's best ever players had long been established, the Californian left-hander having piled up 41 victories on the US PGA Tour, including four Major titles.
Always exciting to watch, he had also established a reputation for becoming one of the most meticulous practitioners in the game with his build-up to the big events, plotting out his strategy and club selection in careful fashion.
Mickelson's Achilles' heel over the years has been his driving accuracy, his nadir coming with his meltdown in the final round of the 2006 US Open at Winged Foot where he barely hit a fairway on his way to a tie for second place.
In pursuit of a rare third consecutive Major win, he squandered a two-stroke lead with three holes to play, double-bogeying the last after hitting the roof of a hospitality tent with his drive and bouncing backwards off a tree with his second shot.
"I'm still in shock," he said after hitting only two fairways out of 14 in that final round. "I just can't believe that I did that. I am such an idiot."
Partly prompted by that meltdown, Mickelson linked up with Harmon the following year in a bid to improve his driving accuracy and the pair have since made significant inroads in that area of the game, and elsewhere.
At his best, Mickelson displays not even a glimmer of a chink in his armour, as his closing 66 at Muirfield proved in such stellar fashion.
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- Jack Nicklaus