"Are you at work?"
Translation:Ты на работе?
one of my Russian profs said that a good indicator on whether to use на or в is whether or not the place is an open space, with some exceptions like работа and аптека. but with most cases with words like стадион, парк, дискотека, etc.... I am not sure if this is useful but yeah
"в работе" also means "work in progress." Like, "Этот проект сейчас в работе" - "This project is currently in work"
So, "Ты в работе" also has a meaning of "You're under construction" - a thing that a soon-to-be father would say addressing his pregnant wife's belly (or rather the guy shaping up in there).