Some people just don't like to talk on the phone. I'm not saying she shouldn't be honest and say she just doesn't want to, but that doesn't imply she does or doesn't love you. You'd probably do the relationship a lot of good if you just accept her the way she is. It just sounds like you are feeling insecure if you insist she talk to you, so if there are other issues bothering you, maybe you need to figure out what else might be going on.
I don't talk to anybody on the phone for 20-30 minutes a day, no matter how much I love them. (I have neck problems, it's possible that her pain keeps her from wanting to hold the phone, or be tied to carrying even that weight around to chat on speaker phone, or she might get too antsy to sit still while talking on speaker phone, after about 5 minutes I'm about to hang up on whomever I'm talking to.)
She texts, and sees you, and talks to you, maybe you should just appreciate what she does instead of what she doesn't.
Happiness will never come to those who fail to appreciate what they already have.