Wow, did I write this post? My partner and I live twenty minutes apart (eighteen minutes with no traffic), we go to different universities, she works part-time and most of my free time is taken up by study. I feel your anguish mate, I know what you're going through.
And I think pigglet's hit the nail right smack bang on the head when he points out that you've taken the phone conversations and made them into a routine, or a chore. When you basically do nothing else during the week but study (my situation) I have very little to say on the phone, and if you couple this with the fact that I HATE talking on the phone, it leads to disaster.
If you live so close to her, but can afford to spend a few hours on the phone every night, I think you should spend the forty minutes driving back and forth and the rest of the time actually being with her. A few minutes on the phone every night perhaps, and once or twice a week if you actually go and see her (and she comes to see you), and I think you'll end up a lot better. If you feel this way about the relationship, chances are she does too.
You've got two choices: break it off with her and hoping this won't happen again with someone else; or take charge of the situation and fix it. Notice I don't say that you should just live it out and hope it changes. Relationship problems don't generally sort themselves out. They don't just sit and stagnate, they fester. And if you think you're hiding your concerns, I'll tell you you're not. People (perhaps men, I don't know), think they hide their concerns, but however obvious they think it is, it's twice as obvious to their partners.
I think she enjoyed the break not because she used it and did crazy stuff, but because she didn't think about the routine of talking on the phone, she got to not stress for a day.
So mate, here's what you've gotta do. Follow pigglet's advice to the letter. Don't rely on the phone, instead use that time to travel and see her, but make a plan. Just as phone calls leave too much dead air, a night without a plan (especially when you are travelling 40 minutes) can often end in frustration. So limit your phone calls, don't acknowledge when you run out of things to say (ie. stuck to the interesting stuff), make the time to actually see her, and tell her why you want to make these changes.
It's late and I've been drinking after finishing an essay, so excuse any weirdness
I re-read this and I'm worried I sound aggressive, but I honestly don't intend to be. Sometimes when I try to speak or type in a motivational "go team!" tone it comes out aggressively. So I apologize! But mate, write back here with your thoughts, and how everything goes