I think you've got that query the wrong way around. You're comparing the encrypted column with the results of the decryption function. You should be comparing the decrypted value with the results of the decryption function applied to the column.
Also, you're not specifying a length for char, you should. do you know what the default is?
Something roughly like this
where Convert(Char[<whatever the string length is>,DecryptByPassPhrase('[PASSPHRASE]',CPR_encrypted)) =
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