East Hampton otherwise now known as famous (2,3,3)
I believe the answer is:
on the map
'now known as famous' is the definition.
(as in putting somewhere on the map)
'east hampton otherwise' is the wordplay.
'east' becomes 'e' (abbreviation).
'otherwise' indicates an anagram.
'e'+'hampton'='ehampton'
'ehampton' anagrammed gives 'ON THE MAP'.
(Other definitions for on the map that I've seen before include "To be taken into account; charted" , "Informally famous - see atlas" , "Famous or important - consult atlas?" .)