I tend to agree that having a very clear policy about phone calls is important.
Either calls are allowed if there's any struggle at all. This is what my T allows, I can pretty much call for whatever reason. We might talk about it if my T worries that I might become too dependent on him or just call because I miss him. But that so far never meant that I couldn't call anymore.
Or then calls are not allowed at all, but are certainly not reserved for 'particularly bad situations'. I say this because I have experienced very similar things in my life before. I'd get a response from people if I was doing badly enough. So sometimes I'd probably just miss those people and it'd cause me to spiral to a crisis, because then I actually got that contact. Or I'd already be in crisis and had to think about whether to call somebody because I was scared they might not answer, which would make matters worse.

I also kind of feel that if you are in a crisis, a phone call is simply not enough. Either you can see your T in person, which can be scheduled via text or email, or you go to the ER (or of course wait until you can see your T). Therapy on the phone doesn't work well, you don't see the person and can't judge how they're currently doing.