If nothing is blocking the mic, it could be a permissions issue This article looks at all the different reasons an iPhone microphone ... This might include Bluetooth headsets, earbuds, and headphones.

Occasionally your iPhone's microphone ... don't block the microphone when you're on a call. Unplug accessories and disconnect any devices that are connected via Bluetooth, especially headsets.

When we're reviewing the best Bluetooth headset, we're looking for lightweight models that deliver pitch-perfect audio and crisp, clear microphone pick-ups. In my experience, the Jabra Evolve2 65 ...