I know. It's ok - you can call tomorrow. Or does he have an answering machine you could call and leave a message for him to call you back? (Not sure if that would be better or not.)

As for what to say.... "Hi, this is Neutrino. We agreed to get in touch when you returned from your holiday, and I'd like to book an appointment with you as soon as possible." Doesn't have to be more than that. You could even write it down on a piece of paper so you don't have to worry about losing the words when you're on the phone with him.