That was a long time ago, before Mickelson won his first major at the 2004 Masters and before he wrapped his arms, legs and head around the idea that he had to embrace a links golf strategy rather than fight it.
For most of the last decade, that is exactly what he's done at golf's oldest championship, learning to plot his away around the storied old courses that host The Open, using more brains than brawn.
But for some reason on Saturday at Royal Troon, Phil couldn't help himself. It wasn't some sort of outlandish departure from his strategy during the first two rounds, but it was enough to cost him a couple of shots and see him fall behind Henrik Stenson heading into the final round.
"When I tried to play a little bit more aggressive on the downwind holds, I started to get a little jumpy with my swing,'' Mickelson said after a 1-under-par 70 put him a stroke back of Stenson but five clear of Bill Haas. "I started to get a little bit anxious. That's now how I play my best. Sometimes it's better to not be aggressive.''Seemingly shocking words from Phil, but not as it relates to golf at The Open.
It was here in 2004 that it finally hit him, that Phil being Phil wasn't going to work on these courses, where hard, bumpy ground is not conducive to aggressive shots, that hitting mile-high moon shots often doesn't work against swirling winds.
"This was the first course that I really played effectively links golf,'' Mickelson said. "That's where it really kind of turned for me. This is where it kind of happened. This is where I stopped trying to overpower the golf course, where I kind of accepted playing it as it's designed and not trying to find a new, better way to beat the course other than just straightforward golf. That's probably why I love it so much.''
And yet Mickelson for some reason reverted, at least a little bit, on Saturday. During the opening-round 63, Mickelson hit 16 greens in regulation. It was nearly flawless, with well-placed shots off the tee, many with irons.
Friday's 69 wasn't as strong, but the weather was a big factor. Mickelson hit 13 greens and made a couple of bogeys but still shot under par and held a one-shot advantage over Stenson heading into Saturday.
Much of what Mickelson accomplished in getting to that point was due to other factors aside from just strategy. He worked to take spin off his shots, especially around the greens. He practiced keeping the ball lower to avoid the wind. The great players learn to adjust their ball flight, and after being stubborn about it, Mickelson came to terms with the idea.The results first showed here 12 years ago when he missed the Todd Hamilton-Ernie Els play-off by a stroke. He finished second to Darren Clarke in 2011 at Royal St. George's. Two years later, a week after winning the Scottish Open at Castle Stuart, he went to Muirfield and shot a final-round 66 to blow past the field -- including Stenson -- to hoist the Claret Jug.
Among his 42 US PGA Tour victories and five major championships, that victory is the most surprising -- and perhaps the most special.
Mickelson wasn't in the sentimental mood on Saturday evening. It was a cold, blustery day in Troon and it wasn't getting any warmer as he chatted with the media prior to heading to the practice range.
Things weren't quite right with his swing, and he was determined to get it fixed with his instructor, Andrew Getson.
"I was off today, I didn't have my best stuff,'' he said. "My rhythm was a little quick from the top as we started downwind. I was a little bit jumpy.''
Some of that might be attributed to the position he found himself. Playing alongside Stenson, 40, a long hitter and excellent ball-striker, can do that, too. But he didn't help himself with some of his course management, admitting he got away from his game plan on the front side par-5s, unable to make the birdies he coveted.
"It potentially cost me a couple of shots,'' Mickelson said. "It was a day I tried to force it a little bit.''Mickelson did a good job of staying in the game, recovering from some of his mishaps, making just two bogeys. When he birdied the par-5 16th, he had a one-shot lead on Stenson, but then gave it back with a poor approach that he said was the result of "an awful swing." Stenson birdied the hole, the difference for now.
Nonetheless, a sixth major is within his grasp, one that would tie him with Nick Faldo and Lee Trevino -- only 11 players have won more in history -- and also make him the fourth-oldest major champion at age 46. 
Stenson is a formidable foe, and showed it down the stretch Saturday, playing the last 10 holes in some difficult conditions in even par.
But Stenson, 40, has never won a major, and there is inherent pressure in that, too. He's never held the 54-hole lead in a major, and there is that matter of becoming Sweden's first major champion.
For Mickelson, it seems more about overcoming himself, about finding the form he had the first two days and getting back to the mantra that carried him to victory at Muirfield three years ago -- his last win.
"I know it's not far off because I was hitting it so well,'' he said. "I've been hitting it so good for so long, that I just think one day is an anomaly and hopefully I'll get dialled back in tomorrow.''
Now that's Phil being Phil.