To reboot a Fanvil X5U phone, you can follow these steps:
- Press and hold the "Menu" button on the phone.
 - Press and release the "OK" button while still holding the "Menu" button.
 - Release the "Menu" button when the phone displays the "Reboot" option.
 - Press the "OK" button to confirm the reboot.
 - Alternatively, you can unplug the phone and plug it back in to reboot it.
 
Note: This is just an example of how to reboot a Fanvil X5U phone, and it may vary depending on the firmware version you are using. So please check the phone's manual before attempting to reboot your device.