Having come from a military background where using that is second nature, I'm constantly surprised how rarely I meet civilians who understand it effortlessly. When picking up a package I say "the code is Oscar Foxtrot three-fife" and you see the person processing for a long time to extract the first letter of the word. I've started saying "OF, that's Oscar Foxtrot, 3-5" to help them out.
In other words, asking a customer/consumer to be able to recite something in phonetics is not realistic in most cases.
Fortunately the code already takes this into consideration and removes ambiguous characters.
My experience in the USA is that if I don't include the phrase "as in" (as in "X as in Xray") most people still will not realize what I am doing (the alternative "for" can be confused with the digit.)
I also ask them to check my readback of key information they have given me and vice-versa; usually that works well.
In other words, asking a customer/consumer to be able to recite something in phonetics is not realistic in most cases.
Fortunately the code already takes this into consideration and removes ambiguous characters.