The /ʊ/ vowel is spelled <u>, <oo>, <ou> in could and <oe> in the loan word stoep. The /u/ vowel is spelled <oo>, <u> or <ui> in suit. For many speakers the word suit contains a palatal glide which would make in non-minimal in its various contrasts.
This is a recognised problem for speakers of French, Spanish, Farsi, Turkish, Swahili and probably many others, but with so few minimal pairs, it is not very important. There are also native-speaker accents which conflate these sounds. Many Scottish speakers, for instance, do not have two phonemes in this position.
Interesting pairs include:
looker lucre
The density figure is 0.92%. The set makes 11 semantic contrasts giving a loading of 61.1%.
bull buhl could cooed full fool hood who'd looker lucre look Luke pull pool pulled pooled pulling pooling pulls pools should shooed soot suit sooted suited sooting suiting soots suits stoep stoop stoeps stoops wood wooed