Operation Phi (3,11)
I believe the answer is:
hip replacement
'operation' is the definition.
(type of surgical operation)
'phi' is the wordplay.
I cannot quite see how this works, but
an anagram of 'phi' is 'hip' which is present in the answer.
The remaining letters 'replacement' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hip replacement that I've seen before include "Joint operation" , "Inserted joint" .)