The Windows Phone USB Driver is a piece of software that allows your Windows Phone (or any device running Windows Phone OS) to communicate with a Windows PC over a USB connection. This driver is necessary for tasks such as syncing files, transferring media, backing up data, installing or debugging apps, and performing other management tasks between your phone and your computer.
When you connect a Windows Phone to your PC, Windows will use the Windows Phone USB Driver to recognize the phone as a device and allow interaction. If the driver is missing or not working correctly, your phone may not be detected by your computer.