Most Helpful Girl
Tell her straightaway that when she's with you she needs to spend time with you and not her phone. Also, tell her that if she's not interested in taking your relationship further, she should tell you instead of doing this. I know this will hurt you but at least it'll save you from the heartbreak if there is any in the future.
Most Helpful Guy
How long have you'll been together? The length of a relationship can play a crucial role in these things...