Thanks for your help. I was able to make a little more progress but not there yet.
"Are you running the latest version of iOS on the iPhone 6s? "Yes - it says it's up to date - iOS 13.5.1
"Have you checked to make sure that your vehicle supports Apple CarPlay?" Yes - it supports both Apple CarPlay and Android for Auto
"What happens exactly when you try and connect to your vehicle? Are you trying to connect to your vehicle using Bluetooth or USB connection?" I've tried both ways with different results. When we use my husband's android phone (via USB cable), we are able to use all the functionality of CarPlay (at least what we're looking for). My prime consideration is using the maps/navigation function. When I set the iphone on Bluetooth, it will connect with the "HandsFreeLink" (under "My Devices"); turning it off and on as suggested may have helped that. When I use the USB cable, however, ApplePlay doesn't seem to be able to detect the phone. Further, on Bluetooth I have access to music and the phone functions, but it doesn't respond to Apple Maps. Any suggestions