Why doesn't she call back?

It isn't that weird. I for one well, kinda hate to talk on the phone (yes some girls don't like it believe it or not), it's not weird, but there is a stereotype following us so most people assume we talk all day long. The only two people I have no problem talking on the phone for hours are my best friend and if the case is given my boyfriend and/or guy I'm flirting with. If she answers your messages but not phone calls it can be either one of two things:
1. She's afraid she might run out of things to talk about with you leaving many long awkward pauses, or she's gets too freaked out to talk with you.
2. She might not be that interested in you so texting is fine to pass the time or something but phone calls are more personal.

I have to agree with NotsoBad, just ask her to hang out and see how she reacts.

I'd ask her to hangout and see how things go. if she doesn't respond to you or if she says she has other plans then forget about it she is probably just using your text messages to look popular in front of other guys and/or gals.

I don't know for sure, but it seems to me that a lot of people prefer texts and emails over the phone. It could also depend on her job. I worked a lot on the phone at my last job and reached the point where I HATED to hear a phone ring. I'd unplug my phone if it rang and leave it unplugged for a week. Nothing against the person calling.

If she is responding to you, then I wouldn't be too worried. Just try to get a date and see if she is interested. Plus if she is and isn't a cell phone gal, then you'll be better off since she won't call you all the time when she's bored or trying to look cool.