Hello tirthesh0079,
Welcome to Apple Support Communities!
We want to help get the badge showing the correct number for the Phone app.
Please check for any pending iOS updates, which can help make sure the software is working as expected. This Apple Support page can help get those updates installed: Update your iPhone, iPad, or iPod touch - Apple Support
"Update your iPhone or iPad wirelessly
- Back up your device using iCloud or your computer.
- Plug your device into power and connect to the internet with Wi-Fi.
- Go to Settings > General, then tap Software Update.
- If you see more than one software update option available, choose the one that you want to install.
- Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do."
We hope this helps to quickly resolve the issue causing the incorrect number to show.
If the issue continues, please reach out to an Apple Support Advisor for further assistance: Get Support
Cheers!