I don't know. Why don't you have a nice talk to her about this when you see her next? Tell her that sometimes you can't immediately get to your phone because you're busy at work (or whatever) and could she please not ignore you once you do have time to get back to her.
See how she reacts after you communicate to her and if she's acts the C-word that she appears to be, then dump her and find someone who is actually excited to hear from you and wouldn't ignore you just because you couldn't answer her immediately.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion