The 14-times Olympic gold medallist, still showing no signs of weariness after a draining week of high-pressure racing, powered home over the last lap to win the 100 meters butterfly final in 51.14 seconds.
It was the 27-year-old's fourth consecutive win of the trials after he finished second to Ryan Lochte in the 400m medley final on Monday and ensured he would contest his usual heavy eight-event schedule in London, with the addition of the three relays.
"It was a fun week but there are still a lot of things that need to be perfected," Phelps said.
"It shows that I can do it in a program at a high level again. I was struggling over the last few years."
Lochte sliced half a second off his personal best time to finish third in the 100m butterfly, an event he normally does not swim, but missed out on another berth for London when Tyler McGill grabbed the second qualifying spot.
Lochte, whose rivalry with Phelps promises to be one of the highlights of London, had already qualified in four individual events plus at least one relay.
Missy Franklin, the new spearhead of the American women's team, qualified for a record seventh event in London after winning the women's 200m backstroke.
The 17-year-old from Colorado never gave her rivals a chance as she stormed to victory in 2:06.12 seconds, the fastest time in the world this year and more than a second ahead of runner-up Elizabeth Beisel, who also qualified in the 400m medley.
If Franklin stands on the podium in every race, she will become the first female swimmer from any country to win seven medals at a single games.
"When I think of my biggest dream it would be competing in the Olympics in as many events as I possibly can," she said. "I think I achieved that this week, so accomplishing that biggest dream at this age is so exciting."
Another bright teenage star surfaced from the temporary pool in America's Midwest when 15-year-old Kathleen Ledecky won the 800m freestyle, the longest event on the women's program, ahead of Kate Ziegler.
Ledecky slashed more than five seconds off her best time in leading from start to finish to stop the clock at 8:19.78, the second fastest time in the world this year.
She heads to London as the youngest member of a deeply talented American swim team overflowing with medal contenders.
"Four years ago I never knew how to qualify for an Olympics Trials," Ledecky said.
Anthony Ervin, who won gold at the Sydney Olympics 12 years ago, rolled back the years to qualify second in the 50m freestyle, behind Cullen Jones.
The 31-year-old retired from swimming in 2003 but made a comeback in the hope of making the team for London and he succeeded when got his hand on the wall in the nick of a time.
"I just want to keep this fun train chugging," he said.
The trials wrap up on Monday with just two events, the men's 1,500m freestyle and the women's 50m freestyle where 45-year-old Dara Torres will be bidding to qualify for her sixth Olympics.