Hello Wildbison,
Thanks for that info and for choosing the Apple Support Communities. If I understand correctly, you are unable to use the microphone on a Bluetooth headset when using it with your iPhone. To help with this, see if any of the steps in this Apple resource help:
If you can't connect a Bluetooth accessory to your iPhone, iPad, or iPod touch
Since you said this happens on both your current iPhone and happened on your old iPhone, use iTunes on your Mac or PC to backup and restore your iOS software to factory settings, as this process erases the information and settings on your device and installs a fresh copy of the latest iOS software. Temporarily set up your phone as new to test your issues, and then restore your back up and test the issues again.
How to back up your iPhone, iPad, and iPod touch
Transfer photos and videos from your iPhone, iPad, or iPod touch
Restore your iPhone, iPad or iPod touch to factory settings
Restore your iPhone, iPad, or iPod touch from a backup
Cheers!