Sound works fine outside my vehicle. I’ve deleted the phone and paired it again with car Bluetooth.

 

You're attached via Bluetooth, so you aren't using Apple Car Play. I assume the sound works OK for everything else. You also don't mention what kind of phone. There aren't many places this can be broken. My iPhone remembers the volume setting from the last time it was connected via BT, and it's different depending on the device I'm currently using (which can make it more confusing). I connect my phone to my BT headphones, speakers at home, and my car. Each one has it's own volume setting, and they are ALL different than when I'm not connected to anything.

My first test would be to connect to the car via Bluetooth, and check the volume on the phone. I set mine to full volume, and adjust it using the controls in the car. I think I actually had this same issue when my car was new. I wonder if the default volume setting is full off.

If that doesn't work, check for a volume setting in Google Maps. In my iOS version, there is a "Mute State" selection for Muted, Alerts Only, or Unmuted. Also Guidance Volume Selection (Softer, Normal, and Louder). I also have a selection in settings for "Play voice over Bluetooth", and "Play as a Bluetooth phone call".

If you have an iPhone, try Apple Maps. It's MUCH improved, and seems very accurate. It does take a little getting used to how to use it if you're used to Google Maps, though.

The chances that it's something in the car seem pretty remote, to me.

 

Have you tried using Google Maps via CarPlay?

 

Even though your phone is connected to bluetooth, you also need the cars audio source to be set to bluetooth in order to hear the verbal commands from google maps/waze/apple maps. IF you want to be able to listen to the RADIO, AND hear the google maps verbal instructions, you need to go to the settings within google maps. It'll vary slightly between IOS and Android, but open google maps and tap the Profile icon in the top right corner. Select "Settings" and then "navigation settings". There will be an option for "Play voice over bluetooth" which Woodrow mentioned. Set the voice to play over bluetooth, and you will see than when google maps has something to say, your radio will mute and google maps will "call" the car for a few seconds, and you will hear your instruction. There is no option to my current knowledge in waze or apple maps to have the same functionality.