Phelps will appear at NBAC's Countdown to Gold Gala fundraiser in White Marsh, designed to pull in enough money to cover travel costs for the club's 18 Olympic and Paralympic hopefuls.
That list still includes 2016 contenders Phelps, Allison Schmitt and Chase Kalisz, all of whom will fly in from Arizona, where they've spent the year training with former NBAC head coach Bob Bowman.
The Arizona contingent will be joined by current NBAC head coach Erik Posegay and his crew of Baltimore-based Olympic and Paralympic hopefuls, which includes Becca Mann, Sierra Schmidt, Jessica Long and Becca Meyers.
"There's obviously a lot of excitement because Michael's coming," said John Cadigan, the club's longtime director of operations. "It will be nice to have everyone together."
Cadigan said more than 300 people have already purchased tickets to the event, scheduled for 6-11 p.m. at the Boumi Temple in White Marsh. About 200 auction items will be up for bid during the dinner.
The proceeds will cover travel expenses for all the NBAC swimmers headed to the Olympic and Paralympic Trials this summer. Cadigan said any leftover money will support training for coaches and charitable contributions to Special Olympics and Swim Across America.
The club has held a Gold Gala fundraiser each Olympic year since 2004, when Phelps won his initial haul of six gold medals and two bronze.
As Phelps prepares for a fifth Olympics, his life has never been busier. He'll compete at the Arena Pro Swim Series event in Mesa, Ariz., next week, then head to Colorado for altitude training. After that, his fiancee, Nicole Johnson, is due to have the couple's first child in late May. Then Olympic Trials loom in late June, with Phelps expected to compete for berths in at least three individual events.