Hey there, kartik213.
After reviewing your post, it appears that you're having two issues with your iPhone 11 on iOS 13. Noise cancellation doesn't appear to be working as well as the proximity sensor. When you move the phone from your ear, you have to hit the power button to turn the screen on again. We're glad to help with this.
If you're using a case or screen protector with your iPhone, please remove them, and test both issues.
Restart your iPhone -- If removing the case or screen protector didn't resolve the issues, restart your iPhone and test again once it’s back to the Home screen.
Update your iPhone, iPad, or iPod touch -- If the issues persists, make sure your iPhone is up to date. The latest iOS version is 13.6. If it needs to be updated, be sure to have a fresh backup of your device: How to back up your iPhone, iPad, and iPod touch. Test both of the issues once again.
If you can't update or restore your iPhone, iPad, or iPod touch -- If your iPhone was already up to date, we'd like for you to reinstall iOS. Please back up your iPhone before beginning. The section titled "Put your device in recovery mode and set it up again" will walk you through all the steps to reinstall iOS software on your device. Test the issues again.
Let us know how that goes.
Take care.