Looking on the internet deeply has found these results:

sit at the desk is the most popular phrase on the web.

sit by the desk 1125,000 results on the web	sit at the desk 1599,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
As I sit before the desk like a block of rock, You sit behind desks all day. Now, sit at the desk and keep the line open. You're the guy who sits behind the desk. Well, you want to go over and sit at the desk? When they find Harriet's body on a months, you sit behind the desk. Now, sit at the desk and keep the line open. I'll sit at the desk.	Now, sit at the desk and keep the line open. And from now on you will sit at the desk where you belong! big chair and dark wood, lots of beautiful things. You'll sit me at the desk and suddenly a lighning will strike and tomorrow my picture will be on the front pages with the title Now, sit at the desk and keep the line open. I'll sit at the desk. The first day I became mayor, they sit me down at the desk Well, you want to go over and sit at the desk?

sit by the desk

1125,000 results on the web

sit at the desk

1599,000 results on the web

More popular!

Now, sit at the desk and keep the line open.
And from now on you will sit at the desk where you belong!
big chair and dark wood, lots of beautiful things.
You'll sit me at the desk and suddenly a lighning will strike and tomorrow my picture will be on the front pages with the title
Now, sit at the desk and keep the line open.
I'll sit at the desk.
The first day I became mayor, they sit me down at the desk
Well, you want to go over and sit at the desk?