>Look at places.

There is the door (fake door; unpunched), the safe (empty; unpunched), the magic picture window to the black hole (key item required), the grate (inaccessible; unbimped), and... the ceiling tiles.

Hmm! That's right, you sleuth deductively. There were ceiling tiles, weren't there...?

>Place desk vertically and poke through suspicious ceiling tiles for phone.