Removing or installing a rear camera should not kill a phone...
Is the phone recognized by iTunes when you connect it with a Lightning cable to an iTunes enabled computer? If so, shine a bright flashlight on the screen to see if you have a dim image. A dim image would point to a backlight issue. Not being recognized would point to a more serious logic board issue.
A few things I can imagine happening are:
- You may have damaged the camera connector on the logic board which could be causing a short circuit. Do a good visual inspection.
- You may have accidentally dislodged some components on the logic board, in the area surrounding the connectors. This can happen when we pry the connectors with our nails, tweezers or plastic prying tools. Again, do a thorough visual inspection, preferably with magnification, to see if you notice anything wrong.
- If you have been disconnecting the battery prior to your camera removals, check the battery connector and that surrounding area as well.
So start checking and report back.