The Phillies signed Castillo to a minor league deal March 21, three days after he was let go by the New York Mets. Utley is out with a knee problem and there's no timetable for his return.
"We wanted to give him an opportunity to be a contributor on our club," general manager Ruben Amaro Jr. said. "He was extremely professional about his business, well-liked in the clubhouse. We liked everything about him except we felt like, with the personnel we have here, we're comfortable keeping what we have here moving forward. We decided to let him know that he's been released."
The move leaves Wilson Valdez as the likely starter while Utley is out. It also means Rule 5 pick Michael Martinez has an excellent chance to make the team, along with either Pete Orr or Delwyn Young.
A three-time All-Star and former stolen-base champ, Castillo had lost a lot of range in recent seasons. He reported to the Phillies' spring training camp a full day after he signed, perhaps taking more time to join the team than some expected.
"Basically when we brought him in here, that was a short time," Phillies manager Charlie Manuel said. "We'd already gone through spring training and got to see who we had. The way our team lines up, the fact that Valdez played such a good role for us last year and can play multiple positions and Martinez was very intriguing in spring training, that's about what it was.
"He can play for a period of time, but he does get tired," Manuel said. "I also like that Wilson and Martinez can play all of the outfield positions."
Castillo had two hits, scored twice, drove in a run and stole a base Tuesday night against the Pirates.
The Phillies hope to have Utley back within the first two months of the season. Valdez filled in admirably at shortstop for Jimmy Rollins last season and received positive reviews for his defensive work. He has never played regularly.
Castillo hit .235 last year and sat much of the second half after returning from a heel injury. Already a target of Mets boo-birds, he was among several players competing for the spot at second base this year.