I bought 50 gn storage but still my phone doesn’t have storage What to do??

The storage you have bought is online at iCloud and is accessible to any device signed into it: it's intended for syncing the data on one device onto any others. This store is not actually on your phone: the storage on iOS devices can't be ugraded. Your only options are to remove some data or to buy another phone with more storage.

Please do not confuse iPhone/iPad internal Storage (which cannot be increased) with iCloud Storage.

To better understand the difference, read this support article:--> What's the difference between device storage and iCloud storage? - Apple Support

Regards

Giulio