"Pumpkin I'm alright, there's no need to worry so much about how I'm doing; if something is wrong, I'll call you."
But it depends on what he constantly calls for; my friend constantly call his girlfriend just because he's somewhat untrustworthy when it comes to her potentially doing things she shouldn't.
Sometimes you just have to tell it how it is. Just let him know he's getting a bit too obsessive and to back up, it's not really a big deal. If he's as into you as he's making it seem, he'll listen. He'll want it to work, I guarantee.
He's getting obsessive. Which is good on certain things but.. This.. You gotta talk to him. Ignore his feelings for a while and get it out off your chest.