Call up and ring a Starr (5)
I believe the answer is:
ringo
'a starr' is the definition.
(I've seen this in another clue)
'call up and ring' is the wordplay.
'call up' becomes 'ring' (synonyms).
'and' says to put letters next to each other.
'ring' becomes 'o' (letter resembling a ring).
'ring'+'o'='RINGO'
(Other definitions for ringo that I've seen before include "Beatle Starr" , "The drumming Beatle" , "Beatles drummer" , "Member of group" , "John Paul I (and another) backed" .)