Well I can only give you a bit of advice from my own experience. Firstly all I have to say, is I know how much it sucks to be getting lots of attention from a guy and then all of a sudden out of the blue he stops calling so much and seems to be losing interest! With that said I'm going to give you a couple of reason as to why he isn't calling so much and then some solutions to this delicate problem.
So the first reason why he may be doing this is because he has lost interest in you or is losing interest in you. Plain and simple. I know it sucks to hear it and I know that we can go through this whole denial thing, of maybe he just got busy. But at some point you have to stop kidding yourself.
The one thing that I know about guys, is that you can tell how interested more by how they act rather than what they say. Girls on the other hand, say a lot about how they feel and talk a hell of a lot. Thats how we communicate our feelings. On the other hand, guys show how they feel. So if a guy is calling you all the time, msging you all the time and wanting to spend time with you, then he is interested in you. Full Stop. If it is the opposite of that, he's not calling you and not wanting to hang out, its simply because he doesn't want to.
The second reason that kind of goes along with that, is that guys usually have this cooling off period. Despite what they say, guys love the chase. And the chase becomes too easy if you become too available. I.e. answering all of his calls, being all the time. So by him taking a breather it could just be him wanting to distance himself a bit so that he feels like he can pursue you again.
The best thing that you can do in this situation is to not punish him when he comes back from essentially coming out of his cave. Welcome him, with open arms and act like you've been busy that entire time and hardly noticed that he stopped calling. That will get him in the mode of crap I need to get back to work and start pursuing this chick again.
With that said, you are a wonderful girl I'm sure and you know what you deserve. So my suggestion would to go out and have fun. Spending time on yourself and going out with your girlfriends. Lead a full and busy life so that you don't even notice the time that you are not spending with this guy.
Then if he does start calling again, he will pick up that you do just fine without him and that will probably be more appealing to him. If he doesn't get the msg, well then he just isn't worth your time neways and I'm sure there are plenty of other guys who will want to make those phone calls to you =)
All the best
Hot Alpha Female