Schwu

Reflecting this loss of contrast, Wells uses schwi (the so-called ‘happy-vowel’) and schwu (weak-u), replacing [ɪ] and [ʊ] and giving [ˈhæpiə] and [ˈdʒæɡuə].

OED’s base vowel set for British English also includes [...] the barred-/ɪ/ and barred-/ʊ/ symbols (sometimes called ‘schwi’ and ‘schwu’), but these are not separate ‘phonemes’.