How could Mr.0 not recognize Sanji?
You're thinking on the right track except for the fact that den-den mushis do not imitate those speaking. Den-den mushis do not &quot;take the shape&quot; of their owners. They are customized by the owners to show ownership. Trafalgar's den-den mushi looked like him, so did Doflamingo's. Thats why Mr. 0 could not recognize that it was Sanji on the other side of the line instead of Mr. 3. Also because of plot.
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