Please don't box yourself into that corner, canders. ((((hugs)))) I'm glad you did call, and I want you to continue to call if it's urgent to you. (It doesn't matter at this point if he thinks it's urgent at the time, you can discuss that in the following session. Use him to get through to the next session!)
Now, I won't go so far as Gracey's "men" statement

but I will say that as a therapist he may have been in the middle of something when he took time to call you back.

You don't know that perhaps he was signing a new mortgage on his house, or even intervening with another patient and trying to hospitalize them or something, ok?
Yes, we all want to feel and be treated like we are the T's only patient. (((hugs))) But no one is (unless it's a very wealthy T and a very wealthy patient?)
Why not ask the T why he has that particular item for the agenda Monday? You know (I know you do) that Ts usually plan a basic course of therapy to keep you on track. Life does change things as you go...and you need to be able to tell him when it's time to divert a session or two. With discussion of the topic, he might be able to reveal that perhaps where he's trying to lead you will help with the current issue too? Stranger things have happened.
I'm thinking that your T has a service (human) rather than a electronic message center. Why not talk to him about leaving him a message with that service? Would that have the same outcome for you, to know he knows that you are having a tough time and just wanted to make contact with him?
Hang in there, that's why we say that good therapy is hard work. (((hugs)))