The /ɒ/ vowel is spelled <o>. The /ʊə/ diphthong is spelled <oor> or <our>.
This contrast is between a short vowel and a diphthong. The starting positions are close and there is some potential for confusion, but there are so few minimal pairs that it is not a problem for learners.
Bonn bourn boss bourse bosses bourses Dolly dourly god gourd gods gourds Mod moored Polly poorly