How do I ask my girlfriend's parents about marrying their daughter?

I am looking to ask my girlfriend to marry me here shortly. I got the ring and everything. What I want to know is, I am trying to figure out the best way to ask her parents. I live 6 hours away from them, and I will probably not see them before I was looking to ask my girlfriend. Is doing it over the phone, the suckers way out. Should I do it face to face, or does that really matter?