Buying more storage did not and will NOT add more memory to your iPhone. There is a significant difference between the memory directly on your iPhone and iCloud Storage. All you have done is buy more space in iCloud, which means you can sync more data in the cloud (which you may not need at all). It most definitely did not add space to your phone. If you are out of space on your iPhone, the ONLY way to get space back is to delete things you don't need, such as photos, apps, music, files, messages, notes, email.
Read this --> What's the difference between device storage and iCloud storage? - Apple Support
Ps: You clearly didn't buy an iPhone with enough memory. Next time you buy an iPhone, buy the most memory you can afford, because once purchased, the memory directly on an iPhone is fixed and can NEVER be upgraded.