Same here, with Android Auto on Ford's Sync3.
Seems like Android Auto was actually never used on a car by the developers. Otherwise I don't understand how these behaviors during a call could be intended:
1) you have buttons on the steering wheel but you can't use them to control the call: if you press the hang up/next song button, you get the next song;
2) you have a 6.5" touchscreen display, but it doesn't display the call controls;
3) you have to distract from the driving in order to manage the call (by either navigating on the display or picking up the phone).