Current smartphones are highly optimized for content consumption a.k.a doom scrolling. Nothing serious exists for programming. On top of that, a touch keyboard and hard to reach special characters make programming on a modern smartphone a big chore. I miss the old days of smartphones that had a hardware keyboard with tactile feedback. I used to code up and maintain a PHP based dynamic website circa 2007 with a Sony Ericsson K770i and upload through a J2ME based FTP client that also had the text editor in it. If I remember it correctly it was called MobyExplorer

What's your favorite free programming environment for commonly used smartphones?