iPhone ringer volume increases to max volume when connecting to car

When connecting to car by either Bluetooth or via cable and - or - using the cars built in charging pad, the iPhone ringer/volume automatically increases to 100% and does not go back down when leaving car. Attached is a still pic of a screen recording that shows volume going up on its own. How to stop this ?

sorry - I had to crop it to reduce the file size, otherwise it wouldn’t upload.