Boyfriend/husband hiding things?

I'm not sure if everyone goes through this or it's just a phase. I have been dating my boyfriend for almost 3 years now and at the beginning of our relationship we had issues with his phone and another female we resolved it she finally leaves him alone. We decided no more phones when we are together because its distracting and we wanna spend time together without all the interruptions but recently when I asked to see a picture or a video of us together taken on his phone he pushes it off or says later. When he does show me it's in a different folder on his phone and it's all I see. I dont mind it but he makes it seem really suspicious like if he has other things I'm not suppose to see. I told him how it looks from my perspective and I jokingly say if he has anything else he doesn't want me to see I'll give him a minute to delete and I'll even close my eyes. He ended up just telling me how it's always the same argument that I dont trust or believe him that I'm always thinking negative. Of course I told him I start to think like that when he makes it seem super suspicious.

If there isnt anything to hide why go through making arguments and killing the good vibes?