There's currently no room on the 40-man roster to add players. Jake Arrieta could be moved to the 60-day IL, if he's going to have surgery, which would open one slot.
Players on the 40-man who are on optional assignment, who have not already appeared for Philly this season:
Arquimedes Gamboa - Let's just say he hasn't earned a September cup of coffee (.580 OPS in AA).
Adonis Medina - could get called.
Jose Pirela - probably most likely of these three.
Players who may have earned a September reward, who would have to go on the 40-man this winter or risk being drafted in December:
Deivy Grullon
Jan Hernandez - currently has a broken bone in his hand (sliding into home head first...)
Tyler Gilbert
Darick Hall
I really don't see the Phillies adding anybody else - at least not a prospect - to the 40-man before the end of the season. There are a few older guys who might get added to the bullpen:
Dan Straily
Nick Vincent
But they have one 40-man slot, unless they DFA somebody (or define Morgan, Ramos, or Bruce as done for the season, and assign them to the 60-day).
So don't look for Mickey Moniak, or Austin Listi. They're not Rule 5-eligible; their rewards come next season (if they continue to perform).
Who did I miss?