Hey William,
Have you installed the drivers for your device yet? You would need to go to this page and locate the correct driver for your device. This will allow your UE4 project to deploy to your device.
The drivers are located in the second to last section on both of the list of devices.
After you install the drivers, you should see a screen pop up on your phone asking if you would like to trust this computer. You would always want to click allow so that the phone can sync with your computer.
Let me know if you come across any other errors.
Thanks!