Baseball teams are made up of much more than a 25-man roster. Beyond the regular, everyday roster there are dozens of athletes filling the minor leagues. There's prospects: the guys that will be the superstars of the future like Trevor May and Sebastian Valle. There's also the replacement players like Scott Podsednik and Joel Piniero, who are waiting in the minors until a space needs to be filled.
This look at the Phillies' depth is not solely prospect based (if you want to see a prospect-based list, here is my story ranking the prospect depth in the organization), but instead takes into account everyone in the system from Chase Utley to Chace Numata.