How Do Ask My Boyfriend If He's Cheating?

For a couple of months now I feel like my boyfriend is cheating on me and I dont know how to confront him about it. The reason I feel he is that for a while almost 4 or 5 months he hasnt said anything to me about having when he used to all the time. He only does about 2 or 3 times a month and every time he's texting somebody he doesn't want me to look at his phone. I'm just afraid if I ask him he will blow up and start a huge thing on how I don't trust when I did untill now. Please help!!!