Jimmy dressed in rings? They’re not genuine (7)

I believe the answer is:

phonies

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'jimmy dressed' is the definition.
I can't judge whether this defines the answer.

'in rings? they're not genuine' is the wordplay.
'in' is an insertion indicator.
'rings?' becomes 'phones' ('phone' can be a synonym of 'ring').
'they're not genuine' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'phones' placed around 'i' is 'PHONIES'.

Can you help me to learn more?

(Another definition for phonies that I've seen is " These are artificial".)

I've seen this clue in The Times.

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