But instead of a Speedo, he wore a tuxedo.
Katie Hoff sat next to him, wearing a purple dress, and two swimmers - perhaps the best male and female swimmers in the world - began the evening with a brief news conference attended by a small horde of media, some of whom had traveled from as far away as China. Both Phelps and Hoff said that the Olympics, which begin Aug. 8, could not get here soon enough.
The evening also represented something of a homecoming for Phelps, a Rodgers Forge native who has been living and training in Ann Arbor, Mich., the past four years. In late April, NBAC announced that Bob Bowman, Phelps' coach, would be resigning from his job as head coach at the University of Michigan and taking over as the club's CEO after the Olympics. Phelps confirmed what was widely believed to be the case: He'll follow Bowman wherever his coach goes.
"I'm not going to swim for anybody else," Phelps said. "I think we can both help [NBAC] go further. I'm definitely going to be [in Baltimore] next year."
The fundraiser featured a live band, a raw bar, and a silent auction that allowed attendees to bid on virtually everything: a week in Hilton Head, S.C.; a signed Phelps swim cap; teeth whitening sessions; even lunch with Hoff. It also took the time to honor the club's past Olympians: gold medalists Teresa Andrews, Anita Nall, Beth Botsford and Phelps, as well as Olympians, Pat Kennedy, Jill Johnson, Whitney Metzler and Hoff.
"I can remember when I first came here, just looking at all the Olympians who had their pictures on the wall and thinking, maybe someday," Hoff, from Towson, said. "At that point, I wasn't even in contention for anything like that. But this place truly transformed me. I owe it all to this place."