You could just ignore her, although if you go from responding like everything is normal to not talking to her at all, it kind of sends mixed messages. I'm not sure what your issues were with the relationship, who broke up with who or whatever, but if you explain to her that this is what you both agreed on and that you need your own space to figure things out and she should respect that. When she calls and texts you, that's not respecting it. If you lay it out like that, and if after a couple of warnings she doesn't get it, then you just completely and utterly cut her off for good. But if you explained it to the best of your ability, you should have nothing to feel bad about in that respect, even though it clearly sucks that you guys are broken up.
You need this space on your own so you can let the attachment to her die and deal with your emotions. Use this time to focus on things that are important to you. Maybe catching up with some family and friends that you were probably seeing less of due to the time invested in your relationship. I'm sure you would like nothing more than to have great standing in those relationships right before you leave for active duty. Instead of your relationship and how to make it work again. You guys both need time apart and it takes time to put all that behind you if you ever to give it another shot anyway.
Good luck with your service. Come back safely.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.