Hello there, Kevin.
It sounds like your iPhone 6 plus is not being recognized in iTunes on your Windows computer. The following Knowledge Base article offers some great, in-depth steps for troubleshooting:
iPhone, iPad, or iPod not recognized in iTunes for Windows - Apple Support
Turn off your computer and your iOS device or iPod, then turn them on again.
Check to make sure that you've installed all required updates for your computer.
Check that you have the latest version of iTunes installed on your computer.
If you connect your iPhone, iPad, or iPod touch to your computer and see "If you have not connected your iOS device to this computer before, unlock the device and tap Trust," make sure that your device trusts the computer.
If you use Windows XP and you see the trust alert on your device repeatedly, make sure that you installed iTunes. Learn how to resolve a repeating trust alert when using Windows XP. You might need to reset the lockdown folder.
Verify that the 30-pin to USB cable or Lightning Connector to USB cable is free of debris and not damaged. If another cable is available, test with that cable instead.
USB cables that are bundled with third-party products or accessories might work only to charge those products and might not transmit data. Also, if you're using a third-party case or extended battery pack, try removing the case and connecting the Apple-supplied USB cable directly to your device.
iOS devices require Apple Mobile Device Support, which should be automatically installed with iTunes. To verify whether it is installed, follow the steps appropriate for your Windows operating system below.
- Move the cursor to the upper-right corner and click the magnifying glass.
- Type Control Panel, and press Return.
- Click "Uninstall a program."
- Verify that Apple Mobile Device Support is visible in the list of currently installed programs.
If Apple Mobile Device Support isn't listed, remove iTunes, QuickTime, Apple Software Update, Apple Application Support, then reinstall iTunes.
If you reinstall iTunes, and Apple Mobile Device Support still isn't installed, you can resolve issues installing iTunes for Windows.
Thanks for being a part of Apple Support Communities.
Kind Regards.