iPhone 11 Pro Max causes Destination Assist (Navigation System in Lexus RX 350) to go to max volume when connected to car via Bluetooth.

When I initiate Destination. Assist when my iPhone 11 Pro Max is connect to car via Bluetooth the volume of Destination automatically increases to 46 - 50 blasting us out of the car. Destination Assist work fine if iPhone is not connected to car via Bluetooth. Had it to Lexus twice and they say it is the iPhone because the have connected other phones to system and cannot duplicate problem.