How do I stop freaking out?

I've been with my bf for 3 years and 2 years long distance. Since we've been distance we communicate every day and say good night. Even though we usually talk every day, when I can't get a hold of him for one night I start to freak out really badly. I cry hard for hours, I feel pain in my heart, I can't sleep, and I feel like it's the end of the world until I hear his voice again. Even if I don't hear from him at night he'll end up calling in the morning and usually it's because he lost his phone or forgot it.

This doesn't happen a lot but when it doesn't it's like one of the worst feeling in the world. He knows I get like this so he tries to keep his phone on him all the time. This doesn't have to do with me thinking he's cheating though.

I guess the feeling you can compare it to is when you expect your child or spouse to be home at night and they don't come home...so you call them and don't get a hold of them and you start to feel really bad.

How do I stop feeling this way? It doesn't happen a lot but when it doesn't I feel like I can't take it.

Also, is this anxiety??