Called one in, feeling sorry for (5)
I believe the answer is:
ruing
'feeling sorry for' is the definition.
(to rue is to regret)
'called one in' is the wordplay.
'called' becomes 'rung' (ring can mean to call on the phone).
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'rung' going around 'i' is 'RUING'.
(Other definitions for ruing that I've seen before include "Feeling bad" , "Regretful" , "Bitterly regretting" , "Feeling sorry for" , "full of remorse?" .)