Hi there rohith65,
We understand you're experiencing an issue with receiving notifications for the Phone app, and we'd like to share a resource that can help.
Take a look at it here: Use notifications on your iPhone, iPad, and iPod touch
Specifically, the section below may help:
"If you don't see notifications for a specific app
To get notifications, connect to a Wi-Fi or cellular network. If you still don't get notifications for a specific app, try these steps:
- Make sure that the app supports notifications. Go to Settings > Notifications, select the app, and make sure that Allow Notifications is on.
- If you have notifications turned on for an app but you're not receiving alerts, you might not have Banners selected. Go to Settings > Notifications, select the app, then select Banners.
- Make sure that you’re signed in to your Apple ID.
- Make sure that Do Not Disturb is off.
- If you’ve recently installed an app or restored from a backup, open the app to start getting notifications."
Cheers!