Phenomenal in deep space, perhaps? (3,2,4,5)
I believe the answer is:
out of this world
'space perhaps?' is the definition.
'out of this world' can be an answer for 'space' (I've seen this before). I am unsure of the 'perhaps?' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for out of this world that I've seen before include "setting for space opera" , "Late" , "Astronauts are sometimes" , "Dead" , "fantastic" .)