iPhone 6 microphone not working in "normal" mode

iPhone 6: iOS 8.4: 16GB

Phone has been working fine until we purchased a blue tooth equipped vehicle. After using the phone in the vehicle in hands free (with no problems), the iPhone will not be heard by the far end. Siri hears and answers. In all other modes (speakerphone, headphone/mic, blue tooth), the microphone works fine.

Have reset (factory) as well as restored the phone with no change in symptoms.

The phone is also having other issues: difficulty downloading in Safari, huge number of crash reports.

Have I missed something in troubleshooting or should I take it in for replacement?