how would you represent the sound /y/ if you wanted to write the word new?
If u chose to use the most common spelling used in endings, it would be 'nue', but 'nyoo' would be legible too.
The phonetic alphabet was invented mainly to deal with the unreliable sounds of English letters such as y (funny, supply, cycle, cyclical, yes, bye, ).
Re u/you/yoo/ /ewe/yew, I tried to explain earlier that the main spellings for the /ue/u/yoo/ sound are 'u-e' (or open u) and 'ue':
e.g. use, muse, music, refuse, refusal, confuse, confusion, unit, cute, duty, reduce, salute ....cue, due, argue, avenue....
In the stem of words the open u spelling is fairly dominant, in at least 137 words, with just 26 exceptions:
eucalyptus, ewer, feud, feudal, jewel, lewd, neutral, newt, nuclear, beauty, nuisance, pewter, pneumatic, pseudo, rheumatism,
sewage, steward, suicide, suitable, suitcase, juice, Tuesday,
you/ewe/yew, youth.
In endings the spellings for /yoo/ are less predictable.
At the end of longer words it is mainly -ue (argue, avenue, barbecue - in 16 words)
but also askew, curfew, curlew, mildew, nephew.
In shorter words mainly -ew (chew, few, Jew, new/knew, per, spew, stew, view (review, interview).