Q: iPhone 6 plus camera only shows Black screen and Does not react to commands. Can anyone help?

Have you tried these steps:

If you see a closed lens or black screen when you open the Camera app, try these steps:

1. Make sure that there’s nothing blocking the camera lens. If you’re using a case, try removing it.
2. Force the app to close, then open the Camera app again.
3. Restart your device, then open the Camera app again.
4. If your device has a front and rear camera, try both cameras by tapping (camera swap icon). If you see the closed lens or black screen on only one camera, take your device to an Apple Retail Store or Authorized Service Provider for more help.

FROM

Get help with the camera on your iPhone, iPad, or iPod touch - Apple Support

I am having the same problem. I have tried evrything from rebooting to restoring the phone and nothing has worked. I just got this phone replaced too as the first one had Siri and mircophone problems. I have been an Apple user for years and have never had a problem but this phone sure is making up for it.  This makes me sad.

If you just had the device replaced, did you restore the device from a backup? If so, try restoring the device as new and see if the camera works. While it can happen, generally a replacement device would not have problems. If the camera works after a restore as new and not adding any additional content back, then the problem is in your backup file, not the phone. You would need to sync your content back to the phone individually, not from the backup.

However, if the restore as new does not fix the camera issue, then you have unfortunately received a defective device. Those things can happen, but it is not the norm.