Learn English – What are the words for rank up or down

I would go with one of the following:

An [administrative] assistant (esp. with junior staff)

[Office] support staff (slightly more broad than just clerks, but often used synonymously)

A bureaucrat (esp. with mildly negative connotations)

Clerical staff

But there's nothing wrong with using the word clerk, it's not informal, and it's a widely understood word that would be readily understood by your readers.

-Aha (with lips either open or shut!)

-I see

-ok

-following

-listening

-yes/yep

-Oh really?

-Got it

-Okey Dokey