iOS has excellent speech recognition, either through Siri, or through the microphone button on the keyboard in devices such as thaw the iPad 2, new iPad, iPad mini, iPhone 4S, iPhone 5, And the recent iPod touch devices
This feature, which was introduced in iOS 5, allows hands-free usage of your phone or device.
However, when using Bluetooth in your car or headset or otherwise for phone calls works nicely, but for speech recognition the Bluetooth device often degrades the quality of the speech-to-text translation.
To change quickly between your iPhone’s microphone and your Bluetooth microphone for speech recognition, try this:
- Hold down the home button like you’re going to engage Siri for command.
- To the right of the Siri button you will see a Bluetooth icon lit up if you’re connected to Bluetooth
- Simply tap this button and you will get a selector to choose between your Bluetooth devices and your iPhone for the microphone for speech recognition.
This affects all speech recognition use, either Siri or the microphone button on the keyboard.
See screenshot below: 
Robert Merrill 
hello, have you noticed ever since iOS 14 came out the Bluetooth button to the right Is no longer there, do you know what happened to it by any chance? I’ve tried extensively googling about it and I can’t seem to find an answer
This is STILL a problem on 2022. *sigh* So tired of not being able to choose phone speaker rather than bluetooth for dictation!!!