Apple icloud storage on iphone?

If I buy the 20GB Icloud storage will that allow me to actually have more GB on my phone as a whole so i could still have my apps however I could download more? If that makes sense because it would be better to buy a phone with 8GB because it's a lot cheaper and i could buy the extra storage for a much less cost? Or is the 20GB just for phones that are like 64 GB or something?

It depends how you plan to use all your stuff.

Lets say you spend more money now for the iPhone with more memory built-in. You store stuff on the phone. You can use iCloud for backing up that information in case your phone is stolen/lost/broken so when you get a replacement, all the data is somewhere else (in this case, iCloud), so you restore that infomration to your phone.

OR

You go in light with iPhone memory because you store all the stuff in iCloud. Every time you access iCloud to get your stuff, those are data charges from your service provider. Best if you have a good data plan. Plus iCloud starts at no extra charge, but after a certain amount, Apple starts charging for the space…

Personally, I back up to my computer… And have the bigger memory iPhone…

Don't get it twisted. You're thinking iCloud works like a 20gb SD external memory card in an Android. Not so much. If you think you can have an app on the phone but store all of it's content on iCloud-doesn't work that way. Photos, sure. Even some music and emails, but iCloud isn't an SD card. Works a lot like Google Drive more than what I think you have in mind. Best luck.