Going through phone

I went through my boyfriends phone for the first time ever. I saw some pictures of his ex on there and a picture of her naked . I got bothered and told him about it and he then flipped it on me and started screaming saying I should have not been looking through his personal stuff and that it was a part of his past, he also mentioned I could have asked him instead of doing it behind his back . I personally wouldn’t get upset, if he did it while I’m sleeping in front of me etc because I have nothing “ personal” that I would mind him seeing or idk I just wouldn’t care but I do understand where he was coming from and I apologized . What I didn’t like is how he raised his voice over that and compared me to snake and he mentioned we would have to built trust. Yes, I went trough his phone but overall I’m a good person with a big heart . I honestly feel his reaction was over board but for some reason I feel bothered still by his reaction towards the situation