Ph-uture Phantom: A 32-year-old New York actor, Davis Gaines, will don the mask after Michael Crawford leaves "The Phantom of the Opera" at the Ahmanson Theatre on April 28. The Florida-born Gaines appeared last spring in the Broadway production of "The Phantom" as a vacation replacement for Raoul, the Phantom's rival. Gaines shares another role with Crawford. He toured with Carol Channing in "Hello, Dolly!" playing the young adventure-seeking storekeeper Cornelius Hackl, the same role Crawford played in the movie version of "Dolly." Meanwhile, the American Spirit Foundation will salute Crawford at a cocktail party at the Music Center following his final performance.