Hi,
Did you turn off the option to use your mobile device as a camera in Settings? Even if you disconnect your phone, your PC will still try to use it as a camera if that option is enabled. To stop this, go to Settings > Bluetooth & Devices > Mobile devices > Manage devices, then in the window that opens, switch off Use as a connected camera under your mobile device. Once that is off, even when you connect your device, your computer will no longer use your phone camera.