The phrase "hast do" is not a commonly used expression in modern English. However, it was commonly used in older versions of the language to mean "have to" or "must." The spelling "hast" is actually an archaic form of the word "have" and is pronounced [hæst]. The spelling "do" remains the same and is pronounced [duː]. So, when combined, "hast do" is pronounced like [hæst duː]. While not commonly used today, understanding the historic spelling and pronunciation of words can aid in deciphering old texts and literature.