You could use a secure encrypted IRC-like protocol like Pest[0], though.
[0]: https://pestnet.io
[0]: https://pestnet.io
Cached copy here: https://web.archive.org/web/20220915015328/https://pestnet.i...
Reminds me a bit of SILC: http://www.silcnet.org/
Still going to struggle with UX on a phone though...