Hello p_vipinlal,
Let's use the steps below to make sure your iPhone 13 is using the latest iOS 16.0.3:
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. Choose the software update that you want to install. You can choose to stay on iOS or iPadOS 15 and still get important security updates. Or you can choose the option to upgrade to iOS or iPadOS 16.

5. 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.
You can also find those steps in this resource: Update your iPhone or iPad
Afterwards make sure to check for any updates for WhatsApp: How to manually update apps on your Apple device
1. Open the App Store.
2. Tap your profile icon at the top of the screen.
3. Scroll to see pending updates and release notes. Tap Update next to an app to update only that app, or tap Update All.
Updating should help to further isolate a potential software conflict.
If that behavior still persists, do you notice the same behavior during phone calls or with other apps?
If this behavior occurs with just WhatsApp, you'll want to reach out to the developer: How to contact an app developer They'd be in the best position to assist with troubleshooting their particular app.
Take care.