How do I use my iCloud instead of phone storage. I pay for 200g but currently can’t even use WhatsApp it says storage ful😩

iCloud is a syncing service, not a storage service -

What's the difference between device storage and iCloud storage? - Apple Support

Here are some helpful articles that can guide you on how to free up storage space on your phone.

How to check the storage on your iPhone, iPad, and iPod touch - Apple Support

How to check the storage on your iPhone and iPad - Apple Support

Manage your photo and video storage - Apple Support

Manage your photo and video storage - Apple Support

Clear Other storage on your iPhone or iPad - Apple Support

Clear Other storage on your iPhone or iPad - Apple Support