Secretary to call by one or two, working jointly (7)
I believe the answer is:
pairing
'two working jointly' is the definition.
(a pair of people working together)
'secretary to call by one' is the wordplay.
'secretary' becomes 'pa' (abbreviation for personal assistant).
'to call' becomes 'ring' ('ring' can be a synonym of 'call').
'by' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'ring' after 'i' is 'iring'.
'pa'+'iring'='PAIRING'
'or' acts as a link.
(Other definitions for pairing that I've seen before include "outcome of cup draw" , "Couple" , "parliamentary procedure" , "Twosome" .)