Red flag or no

I’m talking to this guy he’s really sweet and nice so far however he is a bit on the sexual side and we started discussing our sex life which I guess is pretty standard. Well I asked if he’d like to talk on the phone and he said he can’t because he doesn’t have any privacy because he lives with his sister. He’s 30 btw and I’m 22. He just moved from Boston which is across the country and is waiting for his loft to be ready so he can move in. I understand not having privacy but that just sounds like an excuse because aren’t you able to step outside or talk on the phone when she’s not home? Red flag or no?