I assume this is a sequel to you r previous thread: http://www.loveforum.net/threads/77843-My-Boyfriend-s-Friend-With-Benefits
Frankly, if you need to see his phone in order to trust him, then there's no point in continuing the relationship. It's not like you've got children and are trying to save a marriage. He's just a boyfriend - and boyfriends who can't be trusted should be quite disposable.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.