I’m having problems with iPhone storage

iPhone storage and iCloud storage are two different things, the iPhone storage can't be increased by purchasing more space and it's what you have on the iPhone memory, so to free some space you have to remove what's on your iPhone you can check it in General>iPhone Storage

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

The iCloud storage is flexible it starts with a free 5GB storage and can be purchased if you need more, it's the space in the iCloud where you can store and sync photos, documents, what's in memory in your apps, mail accounts, your Notes, backups etc and this can be checked and managed in Settings>your name>iCloud>Manage Account Storage

Manage your iCloud storage – Apple Support

Do you mean the iCloud storage or the iPhone storage? I think it can be the iCloud storage in this case you need to look into settings>your name (Apple ID)>iCloud>Manage Account Storage and see if you can remove some data and again photos, or you can buy some more space

You need to delete some apps you don't use, files, photos and store them on an external memory drive, you can see it in settings>general>iPhone storage