Your Battery Stops the Current When It’s Done Charging
Contrary to some beliefs, you can’t overcharge your iPhone and deal damage to the battery. Leaving it charging overnight, or charging on a wireless pad, is totally fine.
Today’s iPhone batteries are built to know exactly when the battery has reached 100% charge, and halt the charging process after that, even when your charging device is still plugged in. There’s nothing to worry about, as long as you have an authorized charging cable and not a fake.