Phelps' expected debut would be one of the highlights on the second day of swimming at the Rio Games, though he'd have to share the spotlight with Katie Ledecky. Ledecky already picked up her first medal of the games, anchoring the women's 4x100 free relay to a silver-medal finish behind Australia on Saturday. Phelps, the most decorated athlete in Olympic history, wants to do his part for the men's relay team. The Australians also figure to be in the mix, especially riding the momentum of an impressive opening night at the pool.