I'm going to break up with my gf over phone
Why would you do this?
I'm extremely busy at the moment and I told her that we need to break up for a while.
I understand the circumstance is uncomfortable for all involved. I think you should take a moment from your schedule and do it in person.
I hate myself for being so bad at breaking-up.
It is normal to be scared or uncomfortable to break up with someone. But Like I said you should do it in person so you both can have some closure.