Complex sentence: With the Phillies, he started in AAA, however was called up to the Phillies' major league team by May of the succeeding year, hitting a home run as his first major league hit in his first game.
Split into simpler sentences: With the Phillies, he started in AAA, but was called up to the Phillies' major league team by May. He hit a home run as his first major league hit in his first game.