How can I get my boyfriend to start calling me again?

He used to call me a couple of times a day, then we had some issues and went through a period of breaking up/getting back together. We used to spend hours on the phone, or at least he would call to see how I'm doing or say he was going to bed. Now he only calls if it's something urgent or if he can't get together on our usual days. (We are together on Wednesdays and Sundays only now because our schedules are so crazy and we work at different times.) But he rarely calls in between those days. I don't know why he wouldn;t want to have anything to do with me on those other days. I know for sure that he's not seeing anyone else, or even going out at all; all he does is go to work and play video games at night.