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?
Right handed; slim front pocket wallet and phone in the right picket, keys in the left. I keep my phone in the opposite pocket as my keys to avoid scratches, and those were in the left so phone went right.
I've basically always used the same pocket as my keys and I've never had problems with scratches. Admittedly, I have my phone in my pocket a lot less these days than I did several years ago, but that's still almost a decade of experience...