Be part of a lot of work I put into pub (4,2)
I believe the answer is:
join in
'be part' is the definition.
(thesaurus)
'lot of work i put into pub' is the wordplay.
'lot of work' becomes 'jo' (I am not sure about this - if you are sure you should believe this answer much more).
'put into' is an insertion indicator.
'pub' becomes 'inn' (an inn is a type of pub).
'i' inserted into 'inn' is 'inin'.
'jo'+'inin'='JOIN IN'
'of a' is the link.
Can you help me to learn more?
(Another definition for join in that I've seen is " (Begin to) take part".)