The Temple of Dagon

The best way to reboot iPhone without power button is with the tool which named Reiboot, the tool is totally free. Yes, you don't need to pay.
The method of use as follows:
1. Download Reiboot to computer.
2. Connect your iPhone to PC and launch Reiboot.
3. After ReiBoot automatically detect the condition of your iPhone. You can either click "Enter Recovery Mode", "Exit Recovery Mode" or use both according to the detecting result to reboot your iPhone.
Click here, you will get more tools about smart moible phone<<<

To reboot iPhone without power button, you can try Tuneskit iOS System Recovery. It is for all iOS users to fix multiple iOS system issues. Like iPhone stuck on Apple logo, black/blue/white screen, boot loop screen, iOS update failure, frozen screen, headphone mode, etc in seconds.

Read more:

iPhone Data Recovery on Mac