I want my girlfriend to stop looking through the photos on my phone, is this okay with you?
Are you seriously checking in with me about it first? Why don't you want her to look through your pictures?
I don't want her to see my activities
If you are doing something that your girlfriend would find objectionable, then you should stop doing that. However, if your girlfriend is invading your privacy, you should talk to her about your boundaries and what you are comfortable sharing.
I'm going to tell her the truth that the kind of girl she is, can't be my girlfriend.
If you are hiding things she can't see then there is a problem. I know it is wrong to snoop though. You both have to work on your own issues first in order to move on with other people.