Greater amount to do over the phone for fool (5)
I believe the answer is:
moron
'fool' is the definition.
(I've seen this before)
'greater amount' is the wordplay.
'greater' becomes 'moro' (I can't justify this - if you can you should believe this answer much more).
'amount' becomes 'n' (N is an example).
'moro'+'n'='MORON'
'to do over the phone for' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for moron that I've seen before include "Clot" , "Fool" , "Halfwit" , "Complete imbecile" , "Blockhead" .)