Learner uncovering top compiler Phi, perhaps (6)
I believe the answer is:
letter
'phi perhaps' is the definition.
(phi is a kind of letter)
'learner uncovering top compiler' is the wordplay.
'learner uncovering' becomes 'l' (I can't justify this - if you can you should believe this answer much more).
'top' means to remove the first letter.
'compiler' becomes 'setter' (both can mean a writer of crosswords).
'setter' with its first letter removed is 'etter'.
'l'+'etter'='LETTER'
Can you help me to learn more?
(Other definitions for letter that I've seen before include "It's one of twenty-six" , "Epistle, missive" , "Written note" , "Item sent - character" , "Written message" .)