Phooey to mum! (4)

I believe the answer is:

tosh

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'phooey to mum' is the definition.
I can't tell whether this defines the answer.

'to mum' is the wordplay.
'mum' becomes 'sh' (both can be used to tell someone to be quiet).
'to'+'sh'='TOSH'

Can you help me to learn more?

(Other definitions for tosh that I've seen before include "Rubbish; shot (anagram)" , "Cobblers" , "Slang nonsense" , "Scottish chum" , "moonshine" .)

I've seen this clue in the Evening Standard.

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