Phone bill addition (3)
I believe the answer is:
fee
'phone bill addition' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for fee that I've seen before include "Payment to a professional for services" , "Sum payable to, say, barrister" , "price" , "(Entry) charge" , "Sum payable to professional person for services" .)