Storage space
I bought space on ICloud but I am still unable to install my apps. It says the device is full
iPhone 7 Plus, iOS 13
iCloud storage has nothing to do with physical storage on the device itself. You need to make room on your phone by deleting some content if you want to download more content.
Take a look at this for some more information.
How to check the storage on your iPhone, iPad, and iPod touch - Apple Support
Bear in mind that using iCloud Photos will help save some space on the device, but you may need the extra iCloud storage of you go that route. Also make sure that you know exactly what you are doing before you enable iCloud Photos.