Hi VladislavKos,
Thanks for reaching out to Apple Support Communities. It sounds like you're having a question about preferred Bluetooth connection when in your car. We're happy to provide some information to assist.
If the call is initiated from the Bluetooth connection in your car, it will continue the connection when leaving a voicemail. However, we recommend checking out the section "Bypass your Bluetooth device for calls" here: Set up and use Bluetooth accessories on iPhone
You can also use the Control Center on your device to quickly switch the Bluetooth connection depending on what you're looking to accomplish. If you use CarPlay check the section "Customize your settings for driving" here: Play music, podcasts, audiobooks, and news in your car
We'd also recommend checking your microphone and detection settings for your AirPods with the help of the guide page and article below.
Change AirPods audio settings on iPhone
Change the settings of your AirPods and AirPods Pro
Should you continue to have any issues, reach out to Apple Support directly to further assist.
Contact Apple Support
Cheers!