Kevin Na managed a 2-under 69 to join Scott McCarron in a tie for second at 12-under-par 272. David Toms, Steve Flesch and Tim Herron were one shot further back at 11-under-par 273.
Mickelson took control of the tournament with a 66 on Saturday that gave him a four-shot edge over Na heading into the final round at the TPC of Scottsdale course. Na closed the gap early on with a birdie at the par-4 first, but Mickelson countered with a birdie at the par-3 fourth.
Mickelson then drained a long birdie putt at the par-3 seventh to increase his lead to five strokes. He sent his drive into the left rough at the par-4 ninth, however, and walked away with a bogey after his approach came up short of the green.
The lefthander recovered at the par-5 13th despite another poor drive. Mickelson hit his tee shot into the desert but played a remarkable second shot just short of the putting surface. Mickelson then got up and down for a birdie to get back to 16 under.
Mickelson's troubles off the tee continued at the par-5 15th when his drive found the water. He took a drop and played his third shot to the left of the green. Mickelson then calmly pitched his fourth shot 3 feet past the hole and made the par putt coming back.
The 34-year-old moved on to the raucous par-3 16th and safely landed an 8-iron on the green. Mickelson two-putted for par and closed out his round with a birdie at the par-4 18th for his first win of the season.
'We had a lot of fun,' said Mickelson, who won this event for the second time in his career. 'The people here have treated us so great.'
McCarron tallied three birdies and a bogey over his first nine holes before chipping in for a birdie at the par-4 11th.
The 39-year-old added an eagle at the par-5 13th and knocked his approach within 14 feet of the hole at the par-4 17th. McCarron ran home the birdie putt en route to a round of 65.
Na cooled off after the early birdie but sank a 10-foot putt for a birdie at the 11th to get to 12 under. Na then played his tee shot into a bunker on his way to a bogey at the 12th and dropped another shot with a bogey at the par-5 13th.
The 21-year-old responded with a birdie at the 15th and picked up a birdie at the 17th to join McCarron in a tie for second.
Kenny Perry carded a 1-under 70 to finish alone in seventh place at 10-under-par 274. Charles Warren followed at 9-under-par 275.
Hunter Mahan and Marc Calcavecchia shared ninth place at 8-under-par 276.
World No. 1 Vijay Singh joined Stewart Cink, K.J. Choi, Jesper Parnevik, John Rollins, Tom Pernice, Jr., Patrick Sheehan and Joey Snyder III at 7-under-par 277.