Start breathing down the phone! (6)
I believe the answer is:
blower
'phone' is the definition.
(informal term for telephone)
'start breathing down' is the wordplay.
'start breathing' becomes 'b' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'down' becomes 'lower' (synonyms).
'b'+'lower'='BLOWER'
'the' is the link.
Can you help me to learn more?
(Other definitions for blower that I've seen before include "Speaking-tube" , "Air mover; telephone" , "Fan - telephone (slang)" , "It produces an air blast" , "Telephone (informal)" .)