A person who is required by their boss to be seen in their chair during normal business daytime hours, even though this may not be productive. Contrast with someone who has a flexible schedule. (desk phantom)
The desk mannequin may often be required to interact with clients or answer phone calls or may be involved in a support operation. The desk phantom on the other hand comes and goes and may be at the desk late in the day and return to work into the wee hours of the night.
Joanne has to get to work by 8, she's a desk mannequin for Compucorp. She'll be available again right after 5 though.