Tory in party pamphlet shows what binds us all (6,8)
I believe the answer is:
social contract
'what binds us all' is the definition.
(society is bound by the social contract)
'tory in party pamphlet' is the wordplay.
'tory' becomes 'con' (abbreviation for Conservative).
'in' means one lot of letters goes inside another.
'party' becomes 'social' (social is a kind of party).
'pamphlet' becomes 'tract' (synonyms).
'social'+'tract'='socialtract'
'con' placed within 'socialtract' is 'SOCIAL CONTRACT'.
'shows' is the link.
(Other definitions for social contract that I've seen before include "agreement for the benefit of all?" , "Arrangements for living together" , "System of human life" .)