The spelling of the phrase "doth on sly" is often confused due to its archaic language and irregular pronunciation. In IPA phonetic transcription, it can be written as /dʌð ɒn slaɪ/. The word "doth" is a contraction of "does" and is pronounced as "duhth". The phrase "on sly" means secretly or covertly, and is pronounced as "on slai". Therefore, "doth on sly" is an old-fashioned way of saying "does secretly". Its unusual spelling may require some extra effort to understand, but it adds to its unique charm for language enthusiasts.