When my iphone 6s is charging my GPS will not talk to me. If it is not plugged in I get voice directions fine.
Not part of the Apple Core… but I think the phone thinks it is communication through the car and no longer the phone. If you have the phone plugged into the car’s USB port, it is not just power, it is a communication connection as well. It wants to use the car’s “hand-free” feature to answer your phone, play your songs and direct the speaker for the iPhone to your radio speakers so you don’t have to hold your phone in your hand while you are driving.
Open your owners manual to the section containing the multi-media, radio and cell phone connection so you can teach yourself all the cool things this car can do with your phone. And so you can avoid the ticket for fiddling with your phone as you drive!
Great answer by Mustangman. One more great example of why I love Apple CarPlay and Android Auto. It solves many small SNAFUs.