Bluetooth plays music, but not phone calls

I have an iphone SE with the latest update (14.4.1). It will connect automatically with the bluetooth module in my car stereo and will play music and sound from other apps (youtube, podcasts, facebook, etc), but when a phone call comes in or I place a phone call, the sound mutes automatically, but the call audio and mic are all on the iphone. Everything functions as it should, except that I cannot place or receive calls through bluetooth - again, the music audio mutes as it should, but the phone call sounds are only transmitted on the iphone. Apparently the SE does not offer the options through the "speaker" button on the call menu on the iphone to select the device. I have reset the network settings to no effect. I have gone through ever setting I could find that obviously affects bluetooth without success. I suspect this has something to do with Apple Carplay, which I do not have.

Is there something I am missing or is this a bug?