A reconstructed version of the language is presented by Michael Fortescue in his Comparative Dictionary of Chukotko-Kamchatkan (2005).
/c/ is a voiceless palatal stop (not the affricate č). /q/ is a voiceless uvular stop.
There are no voiced stops (such as /b d g/). However, there is a series of voiced fricatives, /v ð ɣ ʀ/.
/v/ is a voiced labiodental fricative (like v in English). /ɣ/ is a voiced velar fricative (like the g in German sagen in some dialects, modern Greek gamma, Persian qāf, etc.).
/ʀ/ is a voiced uvular fricative (like r in French). (This is the only sign which Fortescue uses in a different way than the standard IPA does. The usual IPA symbol would be ʁ.)
The entire /t ð n l r/ series is alveolar - i.e. /t ð n/ are not dentals.
There are three nasal phonemes, labial /m/, alveolar /n/, and velar /ŋ/ (like ng in English sing).
There are two semivowels, /w/ and /j/ (= English w and y).
There are seven vowels, the high vowels /i/ and /u/, the mid vowels /e ə o/, and the low vowels /æ a/.
Fortescue, Michael. 2005. Comparative Chukotko-Kamchatkan Dictionary. Trends in Linguistics 23. Berlin: Mouton de Gruyter.