Heard French port is bust, in part (6)
I believe the answer is:
breast
'bust in part' is the definition.
'breast' can be an answer for 'part' (breast is a kind of part). I'm not sure about the 'bust in' bit.
'heard french port' is the wordplay.
'heard' indicates a 'sounds like' (homophone) clue.
'french port' becomes 'brest' (port city in Brittany).
'brest' is a homophone of 'BREAST'.
'is' is the link.
Can you help me to learn more?
(Other definitions for breast that I've seen before include "flesh" , "bust" , "Milk-secreting organ" , "Upper front part of the human torso" , "White chicken meat" .)