The spelling of the phrase "didst duty as" is derived from Shakespearean English. "Didst" is pronounced as /dɪdst/ and is the archaic past tense form of "do." Meanwhile, "duty" is pronounced as /ˈdjuːti/, and it means a moral or legal obligation. The phrase "didst duty as" means that someone has fulfilled their obligation or responsibility, as in "He didst duty as a soldier." This unique combination of archaic language and modern meaning is a testament to the timelessness of Shakespeare's works.