Hey rosita1726,
Thanks for using Apple Support Communities. I can see from your post that you're experiencing varying volumes when you receive calls. This may be expected behavior and I'd be happy to explain why. Your iPhone X includes a feature called Attention Aware which intelligently activates your TrueDepth camera and includes benefits like dimming your display if you aren’t looking at your device or lowering the volume of alerts if you're looking at your device.
You can learn more about this in the link below as well as how to adjust this to better suit your needs.
Face ID and attention aware features (iPhone X)
If you have physical limitations, you can tap Accessibility Options during Face ID setup so that you aren’t required to perform the full range of head motion to capture different angles. Face ID is still secure but requires more consistency in how you look at iPhone X. To set up Face ID, go to Settings > Face ID & Passcode.
For additional security, iPhone X is attention aware, meaning it unlocks only when you look at it with your eyes open. iPhone X can also reveal notifications and messages, keep the screen lit when you’re reading, or lower the volume of an alarm or ringer.
If you don’t want iPhone X to check for your attention, go to Settings > Accessibility. Below Attention, you can turn off:
These settings are turned off by default if you turn on VoiceOver when you first set up iPhone X.
Note: Requiring attention makes Face ID more secure.
Hope this helps.
Regards