And he's surrounded by kids who couldn't care less. The Harford County Boys & Girls Club had been told someone maybe even more exciting is about to join them.
Not exactly. It's Shaquille O'Neal, the towering basketball star who's traveling around the country, challenging other athletes at their own sports for his new TV show. Phelps is his latest target. The physically gifted duo are all over Baltimore this weekend, entourage in tow, filming footage for the episode of "Shaq Vs." that will air Sept. 15 on ABC.
Before Shaq and Phelps splashed each other at the Meadowbrook swim club Saturday, they held court at an Inner Harbor media event and dined together at Red Star near Phelps' Fells Point home. Their swim-off goes down today at Loyola University's aquatic center.
O'Neal, who's about a foot taller than Phelps and more than 100 pounds heavier, wouldn't seem to stand a chance against the multigold medalist.
Even he says so.
"It doesn't matter what you do cause it's not going to work," he says.
Shaq does have a pool at home but mainly uses it to dive for rocks with his kids. ("I'd beat him at that, easily," he jokes.)
As for Phelps, he says for the cameras that he's been losing sleep, fretting about the match. Cameras off, he admits he hasn't really worked out in five weeks.
Though Phelps is also sporting a knee-high injury boot, protecting the ankle he injured in his recent Baltimore car crash, he plays it down, joking the boot "might be fake" to throw Shaq off-game.
Of course even with a sleepless Phelps, with an injured ankle, and maybe in the suit and tie he wore to the news conference, it's still not likely to be much of a race - which is where the handicapping comes in.
Producers talked about everything from making Phelps swim double the pool length, of weighting him down, to actually tying his famous dolphin-kicking feet together. What they do will be a surprise.
After playfully sparring at the news conference - at one point Shaq egged on Phelps to jump into the murky harbor water and get the swim on right there - and then delighting the Boys & Girls Club kids, the two staged some "practice" footage at Meadowbrook.
Phelps swam lazily up a lane as an underwater cameraman in scuba gear struggled to keep pace. Shaq pulled on a tight swim cap and swam in black swim trunks and a tank top. Phelps' coach Bob Bowman advised him on his stroke.
At one point Phelps leans over the side of the pool as Shaq swims, encouraging him to clean up his sloppy stroke and refine his kick.
At another, Phelps tries to teach Shaq how to blow "ring bubbles" in the water, a technique he's mastered that pushes huge air bubbles that he blows from the pool floor.
"I've never seen that in my life," Shaq said of the mushroom cloud-sized bubbles, clearly impressed.
Their spillover entourage included Shaq's assistant in high heels and a very Hollywood dress, a guy who makes the performance-enhancing bracelet Shaq seems to wear everywhere these days, everyone's agents, everyone's publicists, everyone's children.
The crew tried to keep onlookers at bay - insisting Shaq demanded privacy - but dozens of swim club members pressed their noses up to the glass, watching the stars film from the lobby.
The race set today is closed, except for about 100 lucky fans who lined up in the heat Saturday afternoon to claim tickets.
The sweaty gentleman at the front of the line was J.B. Gurley, who, at the prodding of his wife and eager 13-year-old twins, showed up two hours early.
"It's going to be kind of fun," the dad said. "Though obviously it's all about the handicap - otherwise there wouldn't be much to watch."
His kids don't much care about that part.
"It's awesome, just seeing them," gushed his daughter, Taylor, as her brother, Ben, piped in, "And being on TV!"