http://rcuhe6pk7mbmsjk7bwyja5etvjhjvzmc724rnf3piamemvawoi44z7qd.onion/b/res/506.html
There's a bunch of them on IRC2P, but that's dark web IRC, so not really a phone IM client. As for phone apps. There's Briar, Session, and SimpleX. Briar runs over Tor. Session runs over LokiNet. SimpleX is its own thing and uses its own servers, which you can self-host if you want.