Apple has discovered that a limited number of iPhone 6 Plus devices sold between September and January are affected by a manufacturing defect with the back camera. This defect causes photos taken with the back iSight camera to come out blurry. Apple will replace the camera in your affected device for free, if eligible. You can find out if you are eligible for a replacement by typing your serial number into this website, which will lookup if your phone is part of the batch with the manufacturing problem.
If your device is confirmed to be faulty, you can arrange a repair though Apple retail channels or over the phone. Apple will not hand out brand new replacement phones … only replace the iSight camera component within the iPhone 6 Plus. The 4.7 inch iPhone 6 is unaffected by this issue. Check the Apple site for more information.