Hi faithknight,
Thank you for posting. We understand your iPhone volume is sometimes lowering and then increasing. We have a resource that might explain this.
It sounds like you're describing Attention Aware features. See this for more information, including how to test by temporarily turning that feature off: About Attention Aware features on your iPhone X or iPad Pro
Even if you don’t enroll in Face ID, the TrueDepth camera on iPhone X or later, or iPad Pro 11-inch or iPad Pro 12.9-inch intelligently activates to support attention aware features. For example,Â
- When you’re looking at your device, your display will not dim until you stop looking at your device.
- If you're looking at your device, it will lower the volume sound of your alerts.
If you don’t want to use these features, go to Settings > Face ID & Passcode and turn off Attention Aware Features."
Have a good one.