I very rarely ring my therapist, I have only done it like 2-3 times in over a year. I don't really like talking on the phone andmy therapist usually sounds kind of cold and distant on the phone and that upsets me, whereas in real life she is kind and supportive most of the time. Sometimes I have decided not to ring because I ask myself if it would make any difference anyway as what I really want in that moment is to talk to her face to face and a phonecall wouldnt really help so I haven't rang.
I think ringing when you think you can't cope and that talking to your therapist will help you from feeling worse is a good time or when you know there is something they can do that would help.