How to report Bugs on IPhone after doing Software update

Hard to say, but what troubleshooting have you tried to correct the issue. What version of iPhone and which version of iOS are you using?

I've never witnessed this type of behavior with m iPhone. I currently have an iPhone 12 Pro with iOS 14.3. I can use Siri on both my Watch and iPhone and no volume issues. And nothing with the other two either. Have you tried restarting the iPhone, just powering it off and back on? The next step is a force restart, Force restart iPhone - Apple Support, then create a current backup and restore to that backup, Restore your iPhone, iPad, or iPod touch from a backup - Apple Support then finally if necessary because the other steps don't help, restore to factory and set it up as new, not using a backup and test the device. Restore your iPhone, iPad, or iPod to factory settings - Apple Support If none of that works, you can contact Apple Support using the Contact Support link at the top of the page here.

Bugs are reported through the feedback link, Feedback - iPhone - Apple

However, what you may determine to be a bug may not be that. Try describing what the problem is and see if this is something that can be solved, and not really be defined as a bug.