The only affect paying has, that i'm aware of, is in the chat rooms (which you can't access from your phone anyways). Donating allows you privileges there. But i know of no need to donate for anything in forums.
I know some people have problems uploading pics from their phones.
It's just a guess, but perhaps you're having trouble posting videos because the links are for mobile? I don't know. Perhaps, for pics, try using the 'full site' option and see if that makes it easier.