Wondering whether you are still using iOS 11 on your iPhone 6 Plus: If so, you can likely update to the newest compatible iOS 12 version: try Settings > General > Software Updates
(About iOS 12 Updates - Apple Support says iOS 12.5.7 is the latest)
Also wondering what happens if you follow Apple support's guidance in their (link below) article:
(NB: Is for iOS 17, or, for accurate info. choose your iOS version at the top of the article
Use your vehicle’s built-in controls to control CarPlay - Apple Support
Eg: For iOS 17 says:
(1) You can also search for a location, use locations you saved as favorites and in collections, and find nearby attractions and services.
Siri: Say something like:
- “Find a gas station”
- “Give me directions home”
- “Take me to the Golden Gate Bridge”
- “Find a charging station”
- “Find coffee near me”
______
"Or (2)
you can use your vehicle’s built-in controls to open Maps in CarPlay and select a route.
Note: If you’re viewing CarPlay Dashboard and Maps doesn’t appear in the recent apps list on the left, tap to see pages of all of your CarPlay apps, including Maps.
- With Maps open in CarPlay,
- Select Search, then select to speak a search phrase, or select to use the onscreen keyboard (if available). You can also select a destination from a category of nearby services, such as Parking or Restaurants."
There are more CarPlay tips in the above linked article.
All the best :-)