I use it on my iPhone all the time
Funny you should say that. I made the very post you are responding to (#33 above) on my old iPhone SE2020, small screen and all, sitting in my recliner. I used the mic voice input and then made corrections manually since Siri is not 100% accurate.
Personally I find the FR site entirely acceptable on my phone, and my iPad, and my computers. With one limitation: As you point out, doing hand-coded HTML on a cellphone is tedious because of the tag punctuation.
However, I have done exactly that, many times, e.g. posting to the Windows Ping list I run, with graphics and all the rest, from the phone. Granted, I much prefer doing that kind of work on the tablet or a computer. I've created from-scratch websites for 30 years, and I'm fairly patient by nature, but I do have my limits.
Modern glitzy websites are mostly a disaster on a phone. So-called "mobile friendly" web coding is horse poop unless it's done extremely carefully and tested on a wide range of mobiles. And that costs money, so it rarely happens in reality. Business is tight.
I get where you're coming from. But at this point in FR's lifetime, the 1990's user interface still works for most of the people who still use it, and I would say, it probably works better than a more "modern" interface would, for a lot of the long-time members.
I passed my 20-year FR anniversary the middle of last year. I'm fairly typical of the older members (I'm 74). I spend time on FR because it's quiet. It holds still while I read it, it doesn't scream at me with flashing graphics, it doesn't have ads that cover the content, and it works acceptably on every computer and mobile device I have: phones, tablets, Windows, Mac, and LInux computers.
If I want to visit a site that jumps around, screams at me, and has obnoxious ads, Lord knows there are plenty of those to choose from.
I had ATT so my hotspot worked fine and I could post with my laptop. When I switched to a cheaper provider with the same phone my Hotspot capabilities died. I have been forced to use a mobile for years now and have become quite use to posting here with it . One trick I use is to write something using my phone's note section then copy and post the entire essay here.