The word "wast on the back of" is a colloquial phrase that means "was behind." The spelling of "wast" is interesting because it is an archaic form of the word "was" and was used in Middle English. The IPA phonetic transcription of "wast" would be /wɑːst/, which represents the long "a" sound followed by the "s" and "t" sounds. This spelling makes it clear that the word has two syllables and a specific pronunciation, despite its uncommon usage in modern English.