Central point of service supplied by phone (5)
I believe the answer is:
navel
'central point' is the definition.
(I've seen this before)
'of service supplied by phone' is the wordplay.
'of service' becomes 'naval' (of or relating to the Navy, an armed service).
'supplied by phone' shows a homophone (sound like) (as it might sound over the phone).
'naval' sounds like 'NAVEL'.
(Other definitions for navel that I've seen before include "Variety of orange" , "Umbilicus" , "Bellybutton" , "Tummy button" , "Something to contemplate" .)