iPhone 6 plus camera not focusing

Any protective case around your phone, that might be to near to the camera lens, or has a magnetic clip?

If yes, remove the case and test the camera again.

If it still does not focus, and to rule out a software issue, set the phone back to factory settings, without using a backup and test the camera after that.

If it still does not work, the problem is hardware related and the phone has to be repaired by Apple:

Restore your iPhone, iPad or iPod touch to factory settings