You can send a phone number on WhatsApp and when clicking on it it gives you the option to chat with that number

It seems that ir doesnt have android auto version.

Since I updated my lineage version all gps apps that i’ve tried crash on android auto :(

Is there any alternative that works well on android auto?

The only problem I see with KDE Connect is that you need to pair the devices. Works great if both are yours, but probably its not something you want leave with the default settings if its shared with someone else.