Advice (serious, no mean comments please)

Okay, me and my boyfriend have been together for almost 5 years. He has never had a problem with me touching, holding, looking at his phone. Sometime this year he has been weird with who looks at his phone. 🤔 I asked him why he doesn't want me to look at it, he said he's not sure because he feels like he wants control of something I guess? Because a couple times his brothers have taken his phone and put gay porn on it and messed with him... But! The thing is I'm his girlfriend! I don't want to hurt him at all... I also said you can even watch me look at it... He just keeps telling me he loves me and he's not hiding anything from me he just doesn't like anyone on it anymore, he also said with time it will help him get more comfortable with me on it? And another thing we do not fight, everything is great, but this is really making me upset... I trust him. But it seems like he's hiding something, but I looked at it one time without him knowing a week ago and there wasn't anything on it but some people he was friends with on FB/SC.. No big deal I told him and he deleted them. But now he's making the excuse his phone is dead or he left it at home, etc.