Hi, I have taken the icloud storage of 50GB but phone is showing storage is full. what should I do.

iCloud and Phone Storage are 2 different and separate things.

Renting iCloud storage does not, in any way, affect your iPhone's local storage capacity.

There is no way to increase local storage capacity on iPhone, iPad or iPod.

You will need to delete content from the iPhone to make room.

See here: link-> What's the difference between device storage and iCloud storage? - Apple Support

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