First and foremost, partly represent (5,3)
I believe the answer is:
stand for
'represent' is the definition.
(standing for is a kind of representing)
'first and foremost partly' is the wordplay.
'partly' indicates the answer is hidden within the clue.
'STAND FOR' is hidden in the letters of 'first and foremost'.
(Other definitions for stand for that I've seen before include "champion" , "Take the place of - bear" , "Signify" , "Represent - in upright posture?" , "Represent while on feet?" .)