iPhone ringer volume fades from loud to quiet

That's correct and you have Attention Aware turned on in settings. The reason is once a call comes in and you look at your phone, your phone knows you've engaged with it and it lowers the volume.

Attention Aware can be found in Settings > General > Accessibility > Face ID & Attention > Attention Aware

A feature designed for the iPhone X is that if you are holding the device and are looking at the screen, the volume will be automatically reduced. This is because the phone can recognize that you are looking at it, and it determines that you no longer need the ringtone to be loud at that point. See this from the iPhone User Guide. http://help.apple.com/iphone/11/#/iph646624222 A clip from there.

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. My emphasis added.

You're welcome. Once I figured this out myself, I actually really appreciate it. Especially in the office so I don't annoy others around me.

I NEED YOUR HELP MR rbrylawsk. I be victim by apple Turkey. I waiting for 40 days to sent back my phone.. Any one answer me why victim me. please take care of me.. my mail adress *** I waiting your answer

<Email Edited by Host>

I can't help you. No one here can help you. This is a user to user forum and Apple isn't here. You need to amend your post and remove your personal email address which you have now posted to thousands of users on this user only forum. Use the Contact Support button at the top right of this page to reach Apple Directly for assistance with your issue.

so I don't annoy others around me.

You, annoying? I would never guess! 😝

LOL......Oh No You Di_n't!!