My T does not have staff and will answer her phone only if it's urgent, and I assume that means expected also, as she will tell me ahead of time. I'm fine with it. I wasn't always, and once was very upset when she took a call. I told her I was not happy; then she told me that it was some important medical information she had been waiting on.

Whether a T "should" or not isn't what matters. What matters is what happens between T and the client, in the room. I think that if the T takes calls and the client isn't happy about it, then the client needs to talk with T about that like anything else.