The symbol in the International Phonetic Alphabet that represents this sound is ⟨ɔ⟩.
It also represents the symbol, which can be remembered as an o which has been "opened" by removing part of the closed circular shape.
Pronouncing that vowel as such is subject to correction for non-native speakers aiming at RP.
The contrast between /ɔː/ and /ɒ/ is thus strongly maintained, with the former vowel being realized as close-mid [oː] and the latter as open-mid [ɔ], similarly to the contrast between /o/ and /ɔ/ found in German, Italian and Portuguese.
Shaded areas denote articulations judged impossible.