The fact that he asked you if you wanted his number means he is intrested.......when a man is not interested he will not offer up anything. He will let the women ask and if she does not then he is off the hook.
Since caller id is so popular right now, if he was not interested he would simply not answer the phone. Guys can be callas sometimes but seldom will they continue talking to a girl they are not interested in. Since you are talking once a day, why not ask him out?
Women in todays society are encouraged to ask a guy out regardless of how long they have known each other. And it releases the burden off of the guy who may be a little shy about doing so. Since you have already been intimate the guy has that pressure of worrying if you want to see him again.
I would suggest asking him out for coffee or a drink, you can put it like getting together to talk. Make it early enough that it can move on to dinner if you both want as well. If everything is going well ask him if he wants to grab a bite to eat or see a movie. I would also be up font and honest, that is not saying you should ask for a relationship, but let him know you like him and are attracted to him. Tell him you would like to start seeing each other if he likes. This puts the ball back in his court as well..........if he wants to start dating then he can ask you out sometime. If not then he can come off with a excuse, like he is really busy or something. Men are pretty good at silly excuses so if he pops off with one then you know where you stand.
Life is to short to play the back and forth do we like each other game. You are both adults and as such if you like each other be honest. If not then you are not wasting your time thinking about him.