The spelling of the phrase "Mongolian idiocy spots" is not based on the phonetic transcription of the words. Instead, it is a derogatory term that has no basis in reality and should not be used. However, for the purpose of explaining the phonetic transcription, the word Mongolian is pronounced /mɑŋˈɡoʊliən/, idiocy is pronounced /ˈɪdiəsi/, and spots is pronounced /spɑts/. It is important to use language that is respectful and inclusive of all individuals and cultures.
See under spot.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.