Retiring a number in any sport is one of the highest honors that can be bestowed upon a player, and in 138 seasons of Phillies baseball, only six players have had their number hung up for good.
Philadelphia has an unofficial rule that’s stood for years that only players who have been inducted into the Hall of Fame can have their numbers retired. Robin Roberts, Steve Carlton, Mike Schmidt, Richie Ashburn, Roy Halladay, and Jim Bunning have each been bestowed that honor, but they could be joined by others in the near future.
Arguments have been made to break the rule for Jimmy Rollins, Chase Utley, and Ryan Howard should they not make it to Cooperstown, but their achievements in Philadelphia arguably outmatch those of Halladay and Bunning.