One’s legendary in performing musical phrases back to front (7)

I believe the answer is:

griffin

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'performing musical phrases back to front' is the definition.
I can't judge whether this definition defines the answer.

'one's legendary in' is the wordplay.
'one's legendary' becomes 'griff' (I can't explain this - if you can you should give a lot more credence to this answer).
'griff'+'in'='GRIFFIN'

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(Other definitions for griffin that I've seen before include "Mythical beast" , "Eagle-headed monster" , "Mythical creature" .)

I've seen this clue in The Times.

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