The /ɒ/ vowel is spelled <o>. The /ɔɪ/ diphthong is spelled <oi> or <oy>.
This contrast is between a short vowel and a diphthong. The starting position of the tongue in the mouth is fairly close, but it is not a problem for any learners.
One interesting pair is collie coyly.
The density value is 3.06%. The pairs make 16 semantic contrasts, giving a loading of 66.7%.
clod cloyed col coil collie coyly cols coils con coign cons coigns con coin conned coined conning coining cons coins cot quoit cots quoits cough coif coughs coifs dolly doily dollies doilies John join joss Joyce Lodz Lloyd's moll moil molls moils Ollie oily Sol soil vol voile
John Higgins, Shaftesbury, November 2009