Worker, perhaps, in sheltered US city (5,2)
I believe the answer is:
santa fe
'us city' is the definition.
(I've seen this before)
'worker perhaps in sheltered' is the wordplay.
'worker perhaps' becomes 'ant' (worker is a type of ant).
'in' is an insertion indicator.
'sheltered' becomes 'safe' (synonyms).
'ant' placed within 'safe' is 'SANTA FE'.
(Other definitions for santa fe that I've seen before include "Capital city of New Mexico" , "US city" , "US state capital" , "Capital of New Mexico state" .)