Deliberately ring up person in trouble (2,7)
I believe the answer is:
on purpose
'deliberately' is the definition.
('on purpose' can be a synonym of 'deliberately')
'ring up person in trouble' is the wordplay.
'ring' becomes 'o'.
'in trouble' indicates an anagram.
'up'+'person'='upperson'
'upperson' anagrammed gives 'npurpose'.
'o'+'npurpose'='ON PURPOSE'
(Other definitions for on purpose that I've seen before include "Deliberately, not by chance" , "Deliberately, with firm intent (2.7)" , "Pours open - quite deliberately (2,7)" , "Deliberately, with full intent" , "Deliberately, as intended" .)