I believe that schwa /ə/  this is the first proper phonetic symbol that U.S. students learn. I remember it from elementary school. It’s the one pronounced like “Uh…”

It’s very important because English likes to change ALL unstressed vowels to schwa, which mean that – fun fact – schwa can be represented by any vowel symbol in English spelling!  This is which is why we can’t remember whether it’s “Pocano”,  “Poceno”, “Pocino” or even “Pocono” (hint – only o’s in the correct spelling of the PA mountain chain).