I assume he means people are too poor to have multiple devices, and if you only have one it's probably a phone. That said I'm dubious anyone who only has a phone is doing meaningful coding
The initial version of Copyparty seems to have been written on a phone: https://news.ycombinator.com/item?id=46056869
There is this guy: https://github.com/OXY2DEV/markview.nvim/issues/216#issuecom.... I haven‘t used his plugin, but it seems quite popular (+3k stars). I guess ergonomics don‘t matter so much yet when you are young..