two fact authentication

Calls going to VM has nothing to do with 2FA.

Please check the following.

• Check your DND status - Settings > Focus [Do Not Disturb]; Use Focus on your iPhone, iPad, or iPod touch - Apple Support
• Check BedTime Status - Clock App; Use Bedtime to track your sleep on your iPhone - Apple Support
• Check your Sound Volume; Adjust the volume on iPhone - Apple Support
• Check your Ringer switch; If you hear no sound or distorted sound from your iPhone, iPad, or ...
• Check Call Audio Routing; Call Audio Routing Bluetooth / Speaker / Automatic

Two-factor authentication for Apple ID

If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information. If you recently updated your account, you can unenroll for two weeks. Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure and means that you can't use features that require higher security.