Called for part of ladder (4)
I believe the answer is:
rung
This clue is a double definition.
'called' is the first definition.
(ring can mean to call on the phone)
'for part of ladder' is the second definition.
('rung' is part of 'ladder')
(Other definitions for rung that I've seen before include "spoke" , "Telephoned" , "Part of a ladder" , "Level in a hierarchy" , "Ladder's step" .)