boyfriend ..phone advice?

Okay guys i need some advice here. My bf and i have been dating for almost 5 years now. He doesn't hide me or anything. he has pictures, tags me on things on social media. The thing is that he is very secretive with his phone. never have i gone through his phone because i dont feel comfortable. i trust him. he has a pin and everytime he unlocks it he gets away or tilts his phone so i dont see like i can not touch his phone at all :/ also one time i grabbed it to take a picture and he just snatched it out of my hands and i was like hmm ok... and i asked him about it later on and he just said he's always like that when it comes to his phone. i mean you think he might be hiding something from me?????