Q: iPhone microphone not working after disconnecting headphones

I have Jaybird bluetooth earbuds and an iPhone 6. The headphones work perfectly, but after I turn them off, the microphone in the phone no longer works for things like Siri, dictation, and voice recordings in Messages. Voice calls behave normally. Please assume that I am doing things correctly, because I am. Yes, headphones are off and disconnected. Yes, I've tried restarting the phone. Yes, I've turned bluetooth off completely (not that I should have to).

Still, the microphone does not pick up any sound. Strangely, if I hit record in the Messages app, it records, but it only picks up static. No sound at all.

Any idea what can be causing this or how to fix it?