When do u let a new relationship answer the phone?

When do you start to let your partner answer your phone? For me if we live together then of course they can it's our phone but unless that's the case even if their over often to me it's like a cell phone its still theirs. I wouldnt just start answering phones or even the door at their place even if they asked me to in the past still doesn't feel right. Is that wrong to think?