The sound of a phone (8)
I believe the answer is:
ringtone
'the sound of a phone' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ringtone that I've seen before include "announcement of caller" , "Sound coming from mobile" , "Nitrogen (anag.)" , "Sound of a phone on an incoming call" , "Sound made by a mobile phone" .)