I have DID. We call our Ts frequently. We have 2. Primary T and back up T.

Primary T I talk to 2-5x a week in between session.

Back up T is 1-2x a week. (Primary T and back up T work and consult with each other often)

Back up T despises the phone. So do I... But my kids (inner kids) do not. So they call her a lot to re-establish connection. Usually doing this helps intervene reaching a boiling point. Or, sometimes depending on the conversation, causes it to boil over. The joys of the phone

As a T, I've always left it open for my clients to call me. Several had my cell phone number until my agency changed it's policy and stated we could not long utilize this method. I have several clients that will call and leave a message. If they have something they even think about calling about, I ask them to call. Granted, they understand that if it's a crisis I may not get it right away, that I may be out of the office, etc. And if its at that point to utilize our crisis services.

Anyway, my rule of thumb for myself as a client and as a T, if you think you need to call, call. Unless T says otherwise.