I've been on the board of my community mental health agency and there are larger concerns here that are about more than just the phone ringing during your or anybody else's session.

Some CMH agencies have as part of their mission to serve the community mental health needs through a 24 hour crisis line. Back when funds were plentiful, an agency could afford to staff the line with paid staff, although the costs can be extremely high-- you can add up that you would need at least 3 full time workers and 1 part time worker, salary + benefits. As funds become tight or specific funding for crisis line work is not available, some agencies choose to keep the program (as it saves lives) and spread the duties around appropriate paid staff. So I guess now that you have told a bit more of the story, I understand the context more.

A community mental health center is different than a private therapy office. The CMH center has a broader mission, and they may have to compromise some client services (e.g. outpatient therapy) in service of other needs in the community (crisis services). So I don't think they are wrong from the larger perspective-- yes, I can understand the disruption of your T session as not ideal. But neither is the crisis of another person who likely has no other alternative in your community, and your T's CMH agency has to balance everyone's needs.

It is a fine alternative to ask to be scheduled on a day when she doesn't have the crisis line responsibilities. I suppose that might mean that you would miss a session a week every so often, since she has to have it for a week. You could also choose to go to private therapy establishment that does not have this requirement for their T's. But I just don't agree that the agency is wrong per se, because it's not just about what's best for the center's therapy clients. It's about what's best for the needs of the community, which I think includes the crisis line. Unfortunately social services are not funded at the level they should be, so ultimately I'm sure that the agency would prefer to be able to staff the line with non-therapists, but in this economy and political times I don't see that happening any time soon.