Why my payment method can’t be past to update and i want to buy icloud couse my storage phone is full

Buying iCloud storage will not increase the storage space on your phone. If you are out of space on your phone, you will need to delete something.

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

Get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK)