Saw a video on reddit and the body language of the male jumped out at me - I think there's a lesson here.
The video consists of two clips of a girl chugging beer at a football game. In the second clip, which starts at 14 seconds, if you pay attention to her boyfriend sitting to her right, he is very interested in her phone.
Does that seem like the kind of relationship dynamic you want to have? Do you want to be that poor beta craning his neck to see what someone else is texting her? Why? What are you possibly going to say about it? If you address it in any way or if she catches you appearing to give a shit about it you come off as weak.
Best bet is to switch to "pull mode" meaning: you withdraw attention from her, focus your attention on something else, and stay in that mode until she makes an effort to get you back. And be careful not to associate any emotional state with her previous behavior - don't get mad, don't pout, pretend you didn't even notice.
This would be hard to do at a ballgame if it was just you and her. In any other situation, start talking to someone else, and after a short while you and your buddy should walk off, just leave your girl behind. And when she inevitably comes looking for you and asks why you left, say something like, "aww, did you miss me?" Don't acknowledge the phone at all.