Hi Angela389,
Since Siri is not working in your car, we suggest checking to ensure your iPhone is running the latest software version. Outdated software can cause features to misbehave. These steps should help:
"Update your iPhone, iPad, or iPod touch wirelesslyBack up your device using iCloud or your computer.Plug your device into power and connect to the internet with Wi-Fi.Go to Settings > General, then tap Software Update.If you see two software update options available, choose the one that you want to install.
Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do."More information on updating can be found here: Update your iPhone, iPad, or iPod touch
If your software is updated and you're still experiencing this behavior, try these suggestions next: If you need help with CarPlay.
Hope that helps!