Backlash will only treat Phoenix like a puppy while he's a puppy, for the most part. Although now that I'm thinking about it, he might occasionally drop a hand down on Phoenix's head to ruffle his hair in an I'm annoying and bigger than you so do something about it kind of way.
Who wants to watch Phoenix transform over and over again. For science? It's totally not for pleasure... Whether Phoenix is on Bravo or Foxtrot, as long as he's rooming with either Who or Reaper they will have repeated reasons for interaction! I could see Who getting a little stalker-y with Reaper's roommate, "to get to know the person she shares a room with," but there are reasons for him to do that to his roommate too.
tbh, I saw Graveyard when you wrote Purgatory, so my brain is in sync with yours! We can see how Charlotte and Phoenix get along in game!