GO HERE FOR OLD REDDIT UI: https://old.forum.guncadindex.com/
This UI used to be bugged, with a couple rate-limiting issues among other things. Courtesy of some bugfixes, it's back in action again.
It's called mlmym, and if you ever need the link to it, it's in the sidebar.
If you encounter any bugs or issues with it, please report them here. Note that it might not have all the features the other UIs do as a result of basically just being the Old Reddit interface.
Its a web site. If your flip phone can handle web sites.... then it should be ok.