Call impostor briefly (5)
I believe the answer is:
phone
'call' is the definition.
(phone can mean to call by telephone)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for phone that I've seen before include "Call (someone)" , "Covert monitoring of electronic exchanges" , "Short piece of electronic equipment" , "Call; eg, mobile" , "Mobile, perhaps" .)