On the phone, she could be mistaken for Cyril! (5)

I believe the answer is:

sybil

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'cyril' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?

I cannot understand how the rest of the clue works.

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(Other definitions for sybil that I've seen before include "Dame - Thorndike, English actress" , "Basil Fawlty's wife" , "Female oracle; Mrs Fawlty" , "--- Thorndike, Fawlty" .)

I've seen this clue in the Evening Standard.

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