Be cause of echo in large container (6)
I believe the answer is:
create
'be cause' is the definition.
(I've seen this in another clue)
'echo in large container' is the wordplay.
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'large container' becomes 'crate'.
'e' placed into 'crate' is 'CREATE'.
'of' acts as a link.
(Other definitions for create that I've seen before include "Produce from nothing" , "Bring into existence" , "Compose" , "Make, generate" , "coin" .)