Twice champion Mickelson, who attended the nearby Arizona State University, piled up seven birdies in a flawless seven-under-par 64 at the sun-splashed TPC Scottsdale to strengthen his hold on the PGA Tour event.
The loudest roar of the day came after the American left-hander struck a nine-iron to inside two feet at the par-three 16th where nearly 20,000 fans were crammed into the massive grandstands surrounding the "noisiest hole in golf".
When Mickelson tapped in the birdie putt to move five ahead of the field, the decibel level again spiked as further cheers echoed around the course.
"It's hard to describe," Mickelson, who ended the day by tying the tournament's 54-hole record of 24-under 189, told Golf Channel of the atmosphere inside the ropes at the Phoenix Open.
"It's one of those things you just need to experience with the way the people are here and the size of the crowds at this tournament, unique to any event on Tour.
"It's pretty cool and to have gone to school (university) here, the way they treat me, it's awesome."
FOOTBALL KICKING DISPLAY
Earlier in the day, the fans packed around the 16th hole were treated to an impromptu display of football kicking by Padraig Harrington after the Irishman had eagled the 15th to trim Mickelson's lead, briefly, to three shots.
As the crowd erupted with chants of "Ole, Ole, Ole", triple major winner Harrington place-kicked an American football from the tee and then punted the next few before setting off toward the green.
After Harrington had two-putted from 15 feet for a rock solid par, cheers of "Paddy, Paddy, Paddy" reverberated across the green.
"I have actually thrown an American football before but I've never kicked one before," Harrington said. "I attempted to throw one and I know my throwing is so poor I had better start kicking it."
The footballs were official Super Bowl models and provided by Harrington's equipment manufacturer, Wilson.
"When I kicked a couple out of my hands, I pulled the first couple because I wasn't used to it, then I hit one sweet and actually kicked it over the grandstand," the Dubliner said.
"Once you get used it to it, it's okay," smiled the Irishman, whose 63 was the day's best score and lifted him into a share of third place at 16 under, a distant eight strokes behind the pacesetting Mickelson.
FedExCup champion Brandt Snedeker was alone in second at 18 under after shooting a 65, though his six-birdie display was not good enough to close the gap on the tournament leader
"Obviously you need to shoot low if you want to catch Phil right now," said the fast-talking Snedeker, who has twice finished in the top three in his first three PGA Tour starts of the year.
"Any time you shoot six under par on a golf course you're gaining ground, unfortunately I didn't do that today on Phil.
"I've got to go out and shoot something low tomorrow and hope Phil doesn't have quite as good a day as he's had the last three," added Snedeker, a four-times winner on the PGA Tour.