Yeah you can plug iPhone into computer, which I haven't done for years now. Only reason was to load it up with mp3s.
Last weekend I've tried to do the same without a computer and basically you can only use players like VLC which only allowed me to load single file (playlists are there, but again you have to connect to computer).
Edit: Just tried one more time and you can place files into VLC folder (using Files is a bit tedious tho) and they appear in VLC player. Yay.
It's annoying as hell though--with Android devices you can see Downloads or Pictures or whatever and move things to and fro as you please.
With ios you need a Mac and you are stuck with the 'Photos' app and or otherwise it's some ugly abstraction with weird year_month_day directories all over the place.
Last weekend I've tried to do the same without a computer and basically you can only use players like VLC which only allowed me to load single file (playlists are there, but again you have to connect to computer).
Edit: Just tried one more time and you can place files into VLC folder (using Files is a bit tedious tho) and they appear in VLC player. Yay.