Involuntary response when calling to do with sound of speech (8)
I believe the answer is:
phonetic
'involuntary response when calling to do' is the definition.
I can't judge whether this defines the answer.
'with sound of speech' is the wordplay.
'with' indicates putting letters inside.
'sound' becomes 'et' (I can't justify this - if you can you should believe this answer much more).
'of speech' becomes 'phonic' (I've seen this in another clue).
'et' put inside 'phonic' is 'PHONETIC'.
(Other definitions for phonetic that I've seen before include "Of spelling, corresponding to pronunciation" , "Pinch toe (anag.)" , "(Spelling) as pronounced" , "Relating to the sounds of spoken language" , "representing vocal sounds" .)