list of banned iphone applications

Unfortunately Apple does not disclose reasons behind removing Apps except to the developers of said Apps.

Youtube Downloader Apps generally circumvent Youtubes copyright TOS for uploaded videos as well as Apple's own App guidelines for downloading of copyrighted material.

Most if not all Apps either get removed entirely, or the ability to download videos from Youtube is removed from the App to comply with said guidelines.

Banned from where? By whom? For what reason would they have been banned?

Since you can only really get Apps for iPhones form the App Store, if its there, its not banned.

I don't believe there is a list of Applications that have been banned from the store though.

Those apps were not banned. They were simply removed until they comply with Apple's policies. They can come back once they do so.

The Apps were mostly in the Chinese store however.

You can find the list gathered by SourceDNA here:

https://sourcedna.com/blog/20151018/ios-apps-using-private-apis.html

Its very unlikely you have one of those Apps, as most of them are in Chinese.