I agree with the don't get angry comments. It's so normal to wonder what's out there! If it wasn't, porn wouldn't be the industry that it is.
With things like music videos being so sexual and evocative I think the age for being curious is getting younger and younger. The Internet and access to so much is making young women wonder what's expected of them in a sexual relationship. Could it be that she was trying to learn?
If so, take to her. Less about the physical side of sex and more about the emotional. Perhaps reinforce the importance of being in a loving relationship where you are respected and feel comfortable to be physical.
Use this to to your advantage, as a tool to get closer to her and new ways to relate. Please do not get angry or deny her any access to the phone at all. She will only resent you for it. Instead try to tighten the security settings and reassure her that as she gets older alot more information will become available to her.
If you don't share this information with her, someone else will. Perhaps friends who are ill informed themselves.
Whatever you do, don't make her feel guilty. Take it from a girl who was made to feel like the devil's child when becoming more explorative! It damaged me for years and I was embarrassed about my body and my needs. You want to avoid doing that if you can