Guilt won't get you anywhere, being a Jesus follower is founded on redemption and Grace. Isn't that awesome! So no reason for living in shame.

That said, you obviously don't want to stay in a place where you're having phone sex with your boyfriend. I can agree with you, that's not healthy for your relationship especially if you're trying to follow Jesus together.

One of the top things you can do is get some advisers into your life, whether that's a young adult pastor at your church, a Christian therapist, or just someone who you look up to as a solid mentor. Especially someone that knows both you and your boyfriend!

You are both worth more than this.

Another thing, is you have to look at your own self and figure out why you're vulnerable to this. For a lot of people they just are really insecure and looking for a sense of wholeness from their boyfriend or girlfriend, it's something you're never going to find any dating relationship. Or in a marriage. I'm sure you already know that, but a lot of the time this kind of struggle can be used for good when you use it to help God give you your sense of identity and not your dating partner.