Happ is taking over Chan Ho Park's spot in the rotation while Park will take over Happ's long relief spot in the bullpen. Park struggled through most of his seven starts this season, with the exception of back-to-back starts against the Mets and Dodgers where he appeared to have gotten himself straightened out. In those two starts, Happ pitched 12 innings and had a 1.50 ERA, but in his seven other starts, he's averaged just under 4 1/3 innings per start and has posted a 10.97 ERA.
Happ started four games for the Phillies last season, going 1-0 with a 2.88 ERA and is best remembered for two strong starts against Atlanta down the stretch. The Phillies won both of those games and Happ allowed just two earned run in 12 2/3 innings of work. As a major league reliever, Happ is 2-0 with a 3.94 ERA.
This spring, Happ and Park battled for the fifth spot in the rotation with Park winning the battle and Happ being relegated to the bullpen.
The Phillies currently have 13 pitchers on their roster and it's likely they'll keep all 13 at least through their weekend series with the Yankees. One reason for keeping the extra reliever is to give Happ a chance to build up his arm strength to start. His longest outing of the season so far has been 3 2/3 innings and his highest pitch count has been 50 pitches.
On Sunday, the Phillies announced that they were flipping Cole Hamels and Jamie Moyer in the order, so Hamels would face the Yankees Sunday, while Moyer would miss the Yankees series and pitch against the Florida Marlins. In his career, Moyer has dominated the Marlins, going 12-1 with a 2.84 ERA in 13 starts against them and is 7-0, 1.58 at Dolphin Stadium.