How do I resolve storage issues after purchasing 50GB space on iPhone?

Purchasing iCloud Storage space does not extend your local storage on your iPhone.

You will have to transfer data from the iPhone to your computer and then delete the exported data on your iPhone.

Have a look at the related article:

Manage storage on iPhone - Apple Support

You will get recommendations for saving storage space on your iPhone, if you go to Settings/General/iPhone Storage.

But, if you use iCloud Photos, deleting photos from the iPhone will also delete them from iCloud and all connected devices.

In that case you should transfer data like photos from iCloud to your computer first:

Archive or make copies of the information you store in iCloud - Apple Support

iCloud storage on Apple’s servers (for synchronization and backup( is not the same as device storage.

You cannot expand device storage on an IPhone. If you are running out of thst, you may have to delete things (possibly after copying stuff from your phone to a computer so it will still exist somewhere),

If you are using iCloud Photos and turn on Optimize iPhone Storage, that can free some device storage by letting the phone store reduced-quality, space-saving local versions of some of your photos. But the phone will still try to keep copies of all photos, and the decisions as to when to substitute space-saving copies for full-side ones, or vice versa, will be under its control.

Re: “But, if you use iCloud Photos, deleting photos from the iPhone will also delete them from iCloud and all connected devices.”

Yes. Manually deleting photos is taken as a request to delete them everywhere, and is quite different from allowing the phone to “Optimize iPhone Storage” or not, as it sees fit. Even with that feature, iCloud Photos is a synchronization service, which synchronizes both adds and deletes.