== Possessives == 

 Numerous authorities on American English state that the correct possessive of Phelps is Phelps's. Note that Michael Phelps is an American, and actually this rule should hold internationally as well. 
 This rule applies in general for names that end in "s", and here are some examples: Abrams's, President Adams's, Douglas's, Evans's, Peter Graves's (Mr. Phelps's Impossible Mission Force), Gross's, Hess's, Hopkins's, King James's, John Paul Jones's, Lewis's, Louis's, Morris's, Norris's, Owens's, Parsons's, Weiss's, and Yates's. 
 Furthermore, the same also holds for other names that end in an "s" sound, such as Fox's, Rex's, Sax's, and Morse's.