Left-hander Mickelson birdied three of the last six holes to close with a four-under-par 67 at the TPC Scottsdale, completing a wire-to-wire victory with a record-tying 28-under total of 256 to clinch his 41st PGA Tour title.
The 42-year-old Californian, who never relinquished his grip after taking control of the tournament with a stunning first-round 60, joined Arnold Palmer, Gene Littler and Mark Calcavecchia as triple winners of the Phoenix Open.
Mickelson sank a 14-footer at the 17th for his fifth birdie of the day, then safely two-putted for par at the last before removing his cap and giving a thumbs-up to the fans crammed around the 18th green.
"It's tough," a beaming Mickelson said after sealing his first win on the PGA Tour since the Pebble Beach National Pro-Am 12 almost a year ago.
"I played really good golf and I had to really fight off a charging Brandt Snedeker, who played great. It's a hard thing to do, to win on the PGA Tour and I'm very appreciative and fortunate."
FedExCup champion Snedeker, who birdied four of the first nine holes to pile early pressure on the pacesetting Mickelson, had to settle for second place after signing off with a 65.
Another American, Scott Piercy, was alone in third at 23 under after shooting the second-best score of the tournament, five birdies in his last six holes giving him a sizzling 61.
Mickelson, however, reigned supreme throughout the week and, with his sixth PGA Tour victory in Arizona, he tied fellow American Johnny Miller for the most wins in the state.
"I hadn't won in a while," Mickelson said after matching the tournament record low of 28-under 256 set by Mark Calcavecchia in 2001. "When you haven't won, you want it bad. I was nervous heading into today's round. It means a lot to get back into the winner's circle."
Mickelson, six strokes in front when he teed off in the final round on a cool and overcast morning at Scottsdale, narrowly missed a birdie opportunity from 10 feet at the par-four first.
He then recorded his first bogey of the week after finding a greenside bunker with his approach at the par-four second, slipping to 23 under and five ahead.
Snedeker sank a 12-foot birdie putt at the par-five third to trim Mickelson's advantage to four but the tournament leader immediately responded by draining a 30-footer for birdie at the par-three fourth.
"I had to kind of get control of my thoughts after the first few holes when things were going where I didn't want them to go," said Mickelson.
"I started seeing what I wanted to do with the ball. And then I started to hit some good shots."
Though Snedeker again countered by chipping in from 30 feet to birdie the par-four sixth, Mickelson rebounded with an outrageous birdie putt from 56 feet at the par-three seventh.
The gifted shot-maker, aiming well right of the hole, rolled his ball uphill and watched as it skirted the fringe of the green while breaking left before disappearing into the bottom of the cup.
Mickelson surprisingly lipped out with a five-foot birdie putt at the eighth and one hole later Snedeker cut the lead to three when he coaxed in a 22-footer for birdie to get to 22 under.
A two-putt birdie at the par-five 13th gave Mickelson welcome breathing space, and he also birdied the 15th after getting up and down from a greenside bunker to remain four strokes clear.
Snedeker finished strong with a run of three consecutive birdies from the 15th before he bogeyed the last but Mickelson was always able to stay at least three strokes ahead.