Why apologise? Your example of how you’d answer the phone was perfectly polite and respectful. If people are going to get all unnecessary about whether they’re addressed as Sir or Ma’am, I’d be fucked before I’d apologise for my lack of extra-sensory perception.Quickly and easily?
“Hello, X Squdron office, Corporal Smith speaking, how can I help you?”
<caller identifies themself>
”Sorry Sir/Ma’am/Dïckhëad, sort it out yourself.”