Outfit introducing new phone (4)
I believe the answer is:
ring
'phone' is the definition.
(to ring on the phone)
'outfit introducing new' is the wordplay.
'outfit' becomes 'rig' (synonyms).
'introducing' is an insertion indicator (some letters introduced or inserted into others).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'rig' going around 'n' is 'RING'.
(Other definitions for ring that I've seen before include "Circle; telephone" , "Form circle around" , "Buzz" , "Chime" , "place for fight" .)