For me, I was on Carplay the other day and my wife called. The ring tone was a bit high but nothing out of the ordinary, after I answered I had to up the volume a bit to hear her better but it was all good. Neither her voice nor the ringtone was extremely high. I was listening to music via CarPlay( Apple Music) when she called and music volume was medium.
Do you have the latest software update on your car and iPhone? I have iPhone 14 Pro with latest IOS update.
Side note, I have other issues with CarPlay. The issue I am having is if I am connected via CarPlay vs Bluetooth I am unable to hit the "Call" button when I search for a POI and and view details, reviews, address, and usually there is a phone number where you can click the "Call" button to call the business. This feature only works when the Phone is connected via bluetooth(the call button is dimmed if connected via CarPlay), also the phone signal strength and battery level icons only shows up when connected via bluetooth. I believe this could be an Apply CarPlay limitation, not sure though.