Volume — nothing cooler for speech-maker (5,3)
I believe the answer is:
voice box
'speech-maker' is the definition.
'volume nothing cooler' is the wordplay.
'volume' becomes 'v'.
'nothing' becomes 'o' (looks like zero - 0).
'cooler' becomes 'icebox' (I've seen this before).
'v'+'o'+'icebox'='VOICE-BOX'
'for' is the link.
(Other definitions for voice box that I've seen before include "The informal larynx" , "Organ" .)