How is that? If the battery is charging then logically there must be enough residual power to run the phone. If there wasn’t then the battery would not charge

How is that? If the battery is charging then logically there must be enough residual power to run the phone. If there wasn’t then the battery would not charge at all unless you turned off the phone first, but it obviously does. Also a phone on a charging mat cannot easily be used and the screen will be off most of the time lowering power requirements.