How do I stop pocket dialing from my iPhone 6plus?

I have a brand new (just bought it last night!) iPhone 6plus. I put it in my bag before I left my house this morning and it evidently called a friend of mine 6 times as I was driving! Glad she's an early riser, but it's still not a good thing. How do I make sure this doesn't continue to happen? I have a password set on my phone so I have no idea how it got beyond that.