iPhone plugged in but not charging

Look in the charging port with a torch before anything else. Pocket lint packs in at the back and the cable sits in far enough to light up but not to charge properly. A wooden toothpick scraped gently along the back wall pulls out more than you'd expect - nothing metal. Also check it isn't just holding at 80%. If it says charging on hold, that's the battery protection doing its job, not a fault. Then try another cable and plug.