Novice repair skill + iFixit community = success!!
I bought an iPhone 6 as a salvage device. It had a broken screen. I intended to repair the device and use it with my day job, demonstrating banking software to prospects.
After replacing the screen, I noticed that TouchID no longer worked. The home button worked for navigation. I feared the worst. Maybe ESD? Maybe too rough with the sensor when moving it to the new front panel assembly?
A forum member suggest I replace the home button flex cable. I did that and resolved the non-functional TouchID.
Then, I discovered the phone was stuck in Headphones mode. No sound from the speaker. Volume control only influences headphone volume.
I decided to replace the front camera and sensor cable, the ear piece speaker, and the lightning connector and headphone jack. Doing so resolved the issue with the phone being stuck in Headphones mode. Sound now plays from the speaker. The ear piece works correctly during phone calls.
The phone is now fully refurbished and functional!
Thanks for the iFixIt community, I had potential solutions presented and never gave up hope. I learned a lot about repair and troubleshooting.
Don't give up. Don't panic. Dig in the forums. The answer is there, somewhere.