Necessity to use the phone (4)
I believe the answer is:
call
I believe this clue is a double definition.
'necessity' is the first definition.
(thesaurus)
'use the phone' is the second definition.
(I've seen this in another clue)
'to' is the link.
(Other definitions for call that I've seen before include "Shout; ring" , "That is enough" , "Phone; cry" , "Visit; cry out" , "Phone - demand" .)