Contact group of spies (see above) (4)
I believe the answer is:
ring
'contact' is the definition.
(to contact by phone)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for ring that I've seen before include "Chime" , "Hoop" , "Call; circle" , "something at the jewellery shop?" , "resonant sound" .)