PHOENIX — Michael Phelps is playing down expectations about his return to competitive swimming but the most decorated Olympian of all time, with a mind-boggling 18 gold medals, is finding it tough to sell himself as an underdog.On Wednesday, the 28-year-old fronted a packed media conference on the eve of his eagerly- awaited comeback at a U.S. swimming Grand Prix meet in Mesa, Arizona.He arrived unshaven, a little plumper than normal and with no swimsuit sponsor, and with the news that he had already pulled out of Thursday's 100 meters freestyle heats to concentrate on the 100m butterfly and Friday's 50m freestyle. "I haven't signed any contracts, no one's making me do this. I'm doing this because I want to," he explained. "I'm loving just being back in the water and in a group. I'm even more relaxed than I ever was before. I'm smiling a lot, I'm happier, I'm joking a lot. "I really am the grandfather of your group now. I'm the old man."