Phelps hit 14 more home runs for Seattle in the first half of 1988. Impressed, owner George Steinbrenner of the New York Yankees traded Triple-A prospect Jay Buhner to Seattle in exchange for Phelps, despite already having Don Mattingly and Jack Clark to play first base and DH. With limited playing time, Phelps found it difficult to maintain his production of the previous four-and-a-half seasons, while Buhner went on to become an All-Star and legendary Mariners player. A "Seinfeld" episode in early 1996 ("The Caddy") depicted Yankee fan Frank Costanza (played by Jerry Stiller) as more upset about the Buhner trade than about the supposed death of his own son Phelps only hit 17 home runs for the Yankees before being traded to the Oakland Athletics in late August 1989. The A's won the World Series, but Phelps had just two at-bats in the post-season, with a pinch-hit double in the third game of the league championship series.