But with the London Games looming, the Baltimore swimmer told "60 Minutes" in an interview that will air Sunday that he has gone all-out recently and says he is now approaching the shape he was in before Beijing, where he won an unprecedented eight gold medals.
His coach, Bob Bowman, predicts Phelps will again win multiple gold medals for the United States this summer.
"Oh, for sure," said Bowman, when asked by "60 Minutes" whether his swimmer can win multiple gold medals. But how many? "I don't know, that's up to him."
Phelps told the program he's physically almost where he was before Beijing.
"I kind of feel like my old self again. I'm swimming times like I used to. I'm swimming races like I used to. So everything is coming back to me, what it was, I guess, before '08," he said.
Just a year ago, Bowman said, he was "very worried at that point ... that we had so far to come, he couldn't get back."
Phelps, flush with millions of dollars in endorsement money and perhaps already the best Olympic athlete ever, had to get his head back in the game. He was having trouble getting out of bed.
"It was hard because I didn't know if the passion or the fire was still inside of me and it took a while for me to actually realize it myself," he said. "Bob couldn't tell me, my mom couldn't tell me."
Nowadays he's back in the pool every day and going heavy on weight training and just to be sure, he has added a new training tool: the altitude chamber. The device encloses his bed and provides thin air with the same oxygen content as the air at 8,500 to 9,000 feet. It is expected to improve his endurance.
"It's something that is helping. I am 26 and I don't recover as fast as I have in the past," Phelps said.
For the new, focused Phelps, each morning is another step toward London and he no longer has trouble getting out of bed.
"No. Because one, we're so close. And two, because I am actually enjoying it. I'm swimming well again."