Troop in to collect a share (7)

I believe the answer is:

portion

I'm a little stuck... Click here to teach me more about this clue!

'a share' is the definition.
(I know that share can be written as portion)

'troop in to collect' is the wordplay.
'troop in' can be anagrammed to 'PORTION'.
However, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for portion that I've seen before include "Serving" , "allotment" , "Share, helping" , "A lot of" , "Helping - fate" .)

I've seen this clue in the Evening Standard.

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