No, you’re not wrong to not want to show him your phone. You’re right in that you’ve set a boundary of trust and it should be respected. This guy does not sound like he was any good for you at all. It’s likely you can’t stop thinking about him because you just broke up a few days ago and you still feel the attachment to him. Give yourself some time… like several months’ worth of time. The attachment will likely fade, your thoughts of him will decrease, and I’m sure you’ll feel much better for not having to deal with someone who treats you in this way.

I hope you feel proud of yourself for choosing not to tolerate this kind of treatment, because the fact that you chose to leave an abusive relationship is definitely something to be proud of. A lot of people stay when they shouldn’t.