About to phone, being concerned (6)
I believe the answer is:
caring
'being concerned' is the definition.
(thesaurus)
'about to phone' is the wordplay.
'about to' becomes 'ca' (I've seen this in other clues).
'phone' becomes 'ring' ('ring' can be a synonym of 'phone').
'ca'+'ring'='CARING'
(Other definitions for caring that I've seen before include "Protective or concerned" , "Showing concern" , "Kind, affectionate" , "medical profession" , "Solicitous" .)