The curious thing is that they filled Eyre's roster spot by promoting right-handed starter Kyle Kendrick to the majors. The logical thing would have been to call up left-handed reliever Sergio Escalona, who hasn't done any damage pitching for them in three games this year. He has 2 strikeouts in 2.1 innings and a 0.00 ERA. There are other pitchers on the AAA Lehigh Valley IronPigs (I just like pointing out that there is a team called the IronPigs - I find it confusing and entertaining at the same time) that might make more sense to call up, including relievers Gary Majewski, who was a possibility for the bullpen during Spring Training, or John Ennis, who appeared with the Phillies very briefly last year. Escalona would still have made the most sense, but instead they called up Kendrick.
One possibility is that the Phillies would like to try Antonio Bastardo in the bullpen and give Kendrick another shot in the rotation. But first of all, Kendrick's numbers on the IronPigs (that's right. Pigs... made of Iron) haven't been particularly impressive. In 12 starts, he went 4-4 and had an ERA of 4.03. Also, Bastardo has been solid for the Phillies. He's currently 2-0 with a 2.45 ERA, and in his last outing he allowed only two runs in 5+ innings against the Dodgers. However, in his start against the Dodgers, it appeared that they were starting to figure him out as they faced him. After zipping through the first six batters in the first two innings, averaging four pitches per batter, he allowed the leadoff man to get on base in the third, fourth, and sixth inning, and couldn't even get an out in the sixth. He had thrown over 100 pitches by that point and was relieved by Chan Ho Park (who, by the way, has been pretty good so far as the long reliever). So it's possible that they'd like to move Bastardo to the 'pen to work on some specifics and then return him to the rotation when Eyre returns. In that situation, why not call up Kendrick, who has been a solid member of the rotation in recent years.
The other possibility is that Kendrick is in the majors to be showcased as trade bait. The Phillies are looking to acquire an impact pitcher to replace Brett Myers. There have been rumors of their interest in Boston starter Brad Penny, so it would make sense to call up Kendrick as the Phillies face Boston this weekend. Brad Penny seems like a much better idea that it would actually be. He is injury-prone and has only had a couple really good years. He was great in 2006 and 2007 with the Dodgers, both years he was an All-Star, but in 2008 he only pitched in 19 games. Boston was able to get him because people were wary of his injury history, so they signed him fairly cheaply. He's been decent with Boston, though he's gotten off to a slow start. He's 5-2 in 12 games, but he has an ERA over 5.00 and 44 strikeouts in 66 innings (just over 5 innings per game). Supposedly, the original asking price for Penny would have had to include prospect Jason Donald (not an IronPig... yet). Donald could be an important trading chip for a bigger deal. The Phillies might do better to wait and see who else gets put on the trading block. If the Phillies are really looking for an injury-prone pitcher, they'd be better to go sign free agent Ben Sheets. The biggest issue with that is the fact that the team is already over budget, but when Sheets is healthy, he is a better pitcher than Penny. Given the choice, I'd take the chance on Sheets. But it's still possible they could get a better pitcher via a trade. Either way, it will be interesting to see how Kendrick is used in the majors. Who knows - maybe he'll reclaim his spot in the Phillies rotation.