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.
The density value is very small at 0.76%. The pairs make 6 semantic contrasts, giving a loading of 75%, though that has no significance with such a small set.
Bonn bourn boss bourse bosses bourses Dolly dourly god gourd gods gourds Mod moored Polly poorly
John Higgins, Shaftesbury, November 2009