Coach Bob Bowman said Phelps, whose bid for a record eight golds ended with the team's worst ever showing in the 4x100 freestyle relay on Sunday, had been asked to help pull the team out of their slump.
Phelps responded by finishing equal fastest in the 200 butterfly heats, his favourite event, on Monday. Team mate and defending champion Tom Malchow was fourth.
"We told him (Phelps): 'You've got to get the ball rolling'," Bowman told reporters. "He and Tom did a great job on that."
The U.S. men had to settle for bronze in the relay, behind South Africa and the Netherlands.
Kosuke Kitajima of Japan also beat American Brendan Hansen for the gold in the 100 breaststroke in a time well off Hansen's world record.
Asked what he would tell his squad, head men's coach Eddie Reese said late on Sunday: "Don't do that again."
The U.S. women have so far contributed two silvers and a bronze to the American swimming team's total of eight medals.
One of their biggest hopes, Katie Hoff, rebounded from a poor showing in the 400 individual medley, when she failed to reach the final, by qualifying third in the 200 individual medley heats on Monday.
Breaststroker Amanda Beard, one of two world record holders on the women's squad and who also reached the 200 medley final, said the men's disappointing start would spur them to come back.
"I know that if they are bummed out they're going to use that to fuel up their fire a little bit," she said.
