Instrument that could make mobile ring (5)
I believe the answer is:
cello
'instrument' is the definition.
(cello is a kind of instrument)
'mobile ring' is the wordplay.
'mobile' becomes 'cell' (I've seen this in another clue).
'ring' becomes 'o' (letter resembling a ring).
'cell'+'o'='CELLO'
'that could make' acts as a link.
(Other definitions for cello that I've seen before include "Bowed musical instrument" , "String quartet instrument" , "has strings attached" , "Lloyd Webber's instrument" , "Music-maker" .)