Boyfriend hiding something??

So just recently every once in awhile my boyfriend will take his phone into the bathroom with him while he takes a shower and he’ll lock the door. He’s only done it a couple times but usually he leaves his phone by the bed then gets in the shower? And he sometimes locks the door but not most of the time. Maybe it’s nothing but I’m on my period right now so I’m thinking all kinds of things and putting stuff in my head ugh :( when we first got together he told me he’s against cheating and he would never do it since he was always cheated on. But I’ve also been cheated on in the past so I’m really trying to trust him. Anything I can do to calm my nerves? Anyone else gone through this?