Don't use the built-in map/directions on the iphone, it is notoriously unreliable and flakey.When I use my android Samsung galaxy note 5 if I use the gps to get somewhere I can hear the turn by turn directions through the radio
But when I use my iPhone 6 for gps I cannot hear turn by turn directions through the radio
Is there a way to hear turn by turn through the radio?
Try Google Maps:
Or, even better, Waze
Also, make sure you're in "Bluetooth Streaming Audio" mode