The spelling of the phrase "most hurry up" can be explained using the International Phonetic Alphabet (IPA) transcription. The first word, "most," is pronounced as /məʊst/, with the symbol "ə" representing the schwa sound. The second word, "hurry," is pronounced as /ˈhʌri/, with the stress on the first syllable and the "u" sound representing the "uh" sound. The final word, "up," is pronounced as /ʌp/, with the "u" sound representing the "uh" sound again. Together, the phrase is pronounced as /məʊst ˈhʌri ʌp/.