On your iPhone, go to Settings > Phone > Calls on Other Devices > un-check all Macsthe Mac. Then switch off "allowthe "Allow Calls on Other Devices" toggle switch and restart the phone.
Also worth mentioning: simply switching off the "Allow Calls on Other Devices" toggle switch does NOT solve the problem - the Macs remain in the audio options list even if that option is off. You need to leave the option on and un-check each device before toggling the option off. You may not see the audio choices change until the phone is restarted.