Female friend takes my phone and rubs her butt on it?

I don't mind it, I actually find it cute. She knows I like her and sometimes she'll take my phone and spam it with 100s of photos and just giggle. Or other times she'll take it and just sit on it and rub her butt against it. And when I wonder where it was she'll say "I have it" and get up and look at me with her finger in her mouth and back to it. Why is that?
Female friend takes my phone and rubs her butt on it?
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