It was a test and you failed.
Look at what that conversation demonstrated to her - that other women want you and she has competition. Did your text messages implied that you were being unfaithful to her? No, they did not. For one thing, they occurred before you started dating, for another, you were basically bragging about the fact that other women want you.
She sees this and obviously it freaks her out because she knows you have options. She wants you to commit to her, so she wants you to feel bad about saying that you have options. She wants to shut out the competition, and you fell for it. You felt guilty over something that is not a mistake, not cheating, and not a problem. Yeah, you ripped the phone away - but it was a personal conversation. Are you not allowed to have secrets now? If you had a fight and you told your best friend about it, is that not allowed?
Yes, you did nothing wrong and so did not need to rip the phone away, but the fact remains that it was a personal conversation, and you and you alone decide who to share personal things with.
She was testing you to see if you would cave, and you did. You have known her for what, 3 weeks? And she is already dictating terms to you?
No matter how awesome this girl may seem, you can't let her dictate the terms.
