There are a number of ways this could go. Joe already spoke to many of them in his Royplacements article. Technically, all of those could still happen (though the odds may shift some) if Savery is only up for a few days. One would have to imagine that if the Phillies go the Bullpen game route, they would want Savery available for an inning or two against the Lefty heavy D-backs lineup. So that has him staying through Friday. Any bullpen game, of course, is likely to use 4 or more Relievers, many for multiple innings and you likely don't want to burn all 3 of your LOOGY bullets in one night. With that in mind, it's entirely reasonable to assume Savery could stay through Sunday to help split the LOOGY load with Valdes and Horst. Technically, I suppose, if we are to consider all options, Savery could pitch Friday, be optioned to LHV on Saturday and replaced by Diekman, but that is incredibly unlikely. For one thing flying him cross country for 2 games seems excessive. Secondly, Diekman has struggled hitting the broad side of an aircraft carrier so far this season and should really hang in Triple-A until he gets his control in order.
So Joe Savery is here until next Monday, which is a travel day back to Philly. From there you have a 2 game set against the Indians, another day off, a weekend series at home against the Reds followed immediately by a trip south to play the Marlins, which is the beginning of the time period where a 5th starter comes into play. So we can assume they either add a bullpen arm like Defratus, Diekman, Robles, Stutes, Rosenberg or perhaps Cloyd as a long man. Or they add a bat.
The options are a bit slim as the bats on the 40 man have either struggled, are redundant or both (Valle). There is an open 40 man spot so the Phillies could add someone, but there aren't many obvious candidates there. It would essentially be adding a fungible AAAA guy like Fields (who would be able to spell guys at a few different positions) or Mitchell, who could spell the Outfielders, though no one really needs a break out there since Delmon's been back a week and everyone else has either split time or is young enough to deal with all the playing time.
The other route to go is fan favorite Darin Ruf. Technically, with the Red Sox series looming and the need for a DH, Ruf could stay up for a while, spelling Howard at first, taking the DH role in the inteague series and acting as a power bat off the bench. That would mean a roster shuffle for the Red Sox series to clear space on the active roster for a 5th starter, but that might be as easy as sending Horst or Aumont down for a few days. Ruf isn't killing the ball the way he did last fall, but he's improved enough after a slow start to be usefull for a few weeks. Of course the downside is, he's limited to First, Left and DH. He won't get more than a single start at 1st, he's unlikley to get any time in Left and it would be better to DH Delmon Young and have superior defender Mayberry in Right for the Red Sox series (The Red Sox series being it's own little thing, but I think the Phillies would be nuts not to call up Ruf for Every IL series needing a DH, hope he crushes and become tradeable to the Rays or other teams with less than stellar DH output).
I have another callup I'd like to see the Phillies make. So far Chase Utley has appeared in 32 games (though just the Pinch Hit in one of those), Jimmy Rollins has been in 32 games, Michael Young has played in 31 games. It might be nice to have another player capable of covering a few of those positions to help spell guys, pinch hit, pinch run, etc. Why not Cesar Hernandez? He's on the 40 man already and he's currently sporting a .358/.412/.514 triple slash for the Lehigh Valley Iron Pigs (albeit with a .416 BABiP). He can play both Second and Short, though he's primarily a second baseman, he brings good speed on the basepaths and he's a hot bat right now. Why not take advantage?
The Phillies liked Hernandez enough to protect him on the 40 man and he's rewarded that faith by starting the year red hot. Reward him with a callup for a week. It gives the team a chance to see how he does, sure, but it's mostly a chance to reward a kid and let him know you've noticed his effort. It's not like the other options are great (woohoo, Josh Fields).