iPhone says it is verifying update, but it's stuck on lock screen I can't unlock my iPhone and it has been saying it's verifying the update for hours now. I can't turn it off or restart it because the button is broken. I can't even unlock my iPhone or slide to power off when using AssistiveTouch.

How do I get around this problem?
Let the battery deplete. After the device shuts down on it own, leave it for a few mins and then put it on charge.

If that fails, you might have to repair the hardware or connect it to iTunes / Apple Configurator 2 to update over lightning connection.