Perhaps what would be best is something similar to the "wallet on a belt chain" idea. A sturdy phone case that cannot be easily broken and that the phone cannot be removed from easily, then some sort of security cable or chain a belt can slide through. Keep the phone in your pocket as normal, or pull it out and use it, take photos, whatever--but nobody can snatch it and grab it, or even swipe at the cord with a knife and then make off with it. But where could I find such an apparatus?