Use your phone if you HAPPEN to see something to record while incidentally out and about. If you’re SPECIFICALLY putting yourself out there to protest, document, or obstruct action, it’s insane to bring your actual phone - get a dumb digital camera. It comes with MUCH less liability, and from a purely practical point of view you don’t wind up trying to explain to your phone company why your phone being stomped into bits by a Nazi should be covered by the insurance. It’s just smarter.