I believe Ubuntu 21.04 is "stable" as of today, but it has no Russian phonetic keyboard. All I can find in Hippo is the quaintly denominated "Russian (polyglot and reactionary)", which as far as I can see is identical to the standard Russian.
I hope the Russian phonetic keyboard is just around the corner. It has been on every long-term version of Ubuntu for at least 15 years. It is very useful for non-Russians and for people who type mostly on qwerty boards and only occasionally switch to Russian.