phone freezes while answering whatsapp chat from notification bar

Thanks for your understanding.

Have you tried uninstalling the app and re-installing. Before you do that, but ensure your chat history is backed-up on iCloud along with media content.

Do let me know if that resolves your issue.

Ok. Try this then (Change settings here)

You may get better and prompt responses if you may kindly provide the iPhone Model that you have and the iOS version if it is known to you.

Also please read this...https://faq.whatsapp.com/en/iphone/22025683/?category=5245260