The phrase "hast a do" is an archaic way of saying "have you a lot to do?" The spelling can be explained with the use of IPA phonetic transcription. "Hast" is pronounced as /hæst/ with a short "a" sound and a "st" consonant blend. "A" in this context is pronounced as /ə/ with a schwa sound. "Do" is pronounced as /du/ with a long "u" sound and a soft "d" consonant. Overall, the pronunciation of "hast a do" is /hæst ə du/.