This. My phone reports "moisture detected" or oscillates between charging and not charging when there's crud inside the socket. I mechanically scrape it with the tip of a sharp pair of tweezers when it's lint, or I use the tweezers to swab with little pieces of paper towel soaked in isopropyl alcohol when it's something more nefarious.

I don't even bother turning my phone off, but it's rated as water resistant and so I am pretty confident that there aren't any voltages present when disconnected. Even on non-waterproof phones, though, any voltage persistently applied to pins on an external connector will result in corrosion over time, so it shouldn't be a problem to just mechanically scrape gently with a dry metal needle.