Phone number part (4,4)
I believe the answer is:
area code
'phone number part' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for area code that I've seen before include "Dialling sequence for, eg, a town" , "Regional dialling no." , "Location-specific numbers" , "Telephone prefix assigned to a region" , "Some phone numbers" .)