It could be he didn't look at his phone because he was busy with clients. (My T often doesn't check her e-mail or phone during the day--MC does though.) Or he may have been waiting to see if he got any cancellations to respond, though it would have been good of him to respond to your morning text, if he saw it, and say something like "I don't have any openings right now, but if anyone cancels, I'll let you know."

Your T might think that responding that day was a reasonable amount of time. And he probably couldn't call because he was seeing clients. He did offer to call later at least. I do understand why you're upset, and I'd likely be reacting similarly to you. But I'm just presenting how it might seem from his side--that he wasn't ignoring you, he was just getting back to you when he could. I think you should talk about this with him, maybe ask about what expectations are during a workday, for example.