I would not tell you because I'd be a little worried how you would take it? It does not sound like you are any more honest than he is; he gave you his phone several times at first, not having a problem with your using it but gradually you have had problems with him and what he likes/dislikes and put him on the defensive and now have gone to invading his personal space.

Everyone has their sexual preferences, men especially have visual ones; some like lingerie, some boobs, some shoes/feet. I would not feel threatened by imaginary big women anymore than I'd feel threatened by issues of Playboy. It's a little like trying to control another person's sexual fantasies? Lots of couples play "football team" but who thinks that is related to gang rape? Looking at soft porn, not to the exclusion of having normal sexual relationships, is not an abnormal behavior to me. It might not be very "mature" having it on one's phone but it's his phone, he can have what he wants on there?

He hasn't lied recently. . . that you know about! But it sounds like now you are attuned to whether he'll lie or not and even lies of omission are on your radar and you want the authority/power to decide if he should have told you something or not. I would not have told you about talking to an ex either, if you respond negatively to it as it seems you do (my husband's ex-wife and I are friends).

It does not sound like you are comfortable with yourself that you are trying to make your boyfriend conform to what you would like him to think/be like. I would have laughed at the "how to fatten up your girlfriend" and told him, "Ain't gonna happen" or, "Good luck! Now I know your plans" or I would start an interested conversation with him about what he likes and decide if I wanted to play with him, enjoy a good meal together, him hand-feeding you or something, before sex, something like that. Let go of trying to control him and explore things together, that is the secret of keeping him "with" you. The more you build together, of your own, the less the "outside" things will draw him.