He won't ring when upset and at fault (2,3,5)
I believe the answer is:
in the wrong
'at fault' is the definition.
(I've seen this before)
'he won't ring when upset' is the wordplay.
'when upset' indicates anagramming the letters.
'he'+'wont'+'ring'='hewontring'
'hewontring' is an anagram of 'IN THE WRONG'.
'and' acts as a link.
(Other definitions for in the wrong that I've seen before include "Guilty of error" , "At fault" .)