I'm going to tell my girlfriend to actually watch whenever we watch a movie
Is she watching movies with you in the movie theater?
Yes, that's why I think it's not such a big deal to ask her to actually watch when we watch a movie
If someone is doing something else while others are watching a movie, it is rude and inappropriate behavior since it can negatively affect the enjoyment of the movie to the people around that person. If your girlfriend is not watching the movie while at the movie theater, then it's okay for you to tell her to get off her phone since it bothers other people. If your girlfriend can't maintain good movie theater etiquette then it would be best for you not to go to the movie theater in the future.
Yes, I feel this way too.
If you keep spending your hard earned money it would really be a waste to keep bringing her. Have you ever asked her what movies she might want to see, it could just be she isn't interested in what you like.