Despite being right handed, it feels more comfortable to place my phone in my left front pocket. Maybe because having a wallet in my right pocket predates using mobile phones. What feels most natural for you?
Non-dominant hand holds your phone, so that's the pocket side where your phone should live.
EDIT:
A few people seem to be confused because apparently they use their phone one handed right from the start when it comes out of their pocket. With the size of phones these days i would guess that most people aren't using their phones one handed that way.
Personally I'll use my phone one handed if I'm stationary and after it's fully out of my pocket and securely in my hands, but if I'm moving around it would be drop-city if I just pulled it out of my pocket one handed and started tapping on it.
I assume zillions of people. The holding is the dumb part that either hand can do, the interacting with the screen is the much more active and precise part that obviously is better accomplished with your dominant hand.