They share a division.
Technically, they're sharing a pennant race.
So why do the Phillies and Braves seem to exist right now in separate universes?
In one -- call it Phillies World -- an ace starts every game, September means never losing and the questions all relate to how things will set up in October.
In the other -- that would be Braves World -- the first game in the most important series of the season is started by a guy whose previous biggest game ever was for the Indiana state high school championship. Oh, and he was a third baseman then.