I had the same problem after ordering and installing a complete ifixit front panel for an iPhone 5c. Everything worked fine except the ear speaker. (Note: actually I can't say for certain that the front camera worked as I don't recall trying to use it.)
I tried all the suggestions mentioned above with no joy. Finally decided to take off the front camera/speaker ribbon from the new ifixit front panel and swap in the same ribbon from the defective screen. After doing so, the ear speaker works as it should.
The front camera/speaker ribbon from ifixit is defective/not compatible for some reason.