HTC Desire 530

I have HTC Desire 530. Under bluetooth settings I see "Phone audio" option but wont let me click it. Phone is connected to the car and shows contacts. When I try to call it says "check phone". On the dial screen it shows my contact and momentarily shows a bluetooth button. If you are fast enough you can turn it on but only about 2 % of the time. If you get it, the phone connects and bluetooth works. My spouses phone auto connects. Any suggestions on how to get the HTC phone when connected to stay connected in Phone audio mode?