In article ,
says...

PLLs are feedback loops. Feedback loops are driven by error. In this
case error would show up as distortion.


Well, that's a pretty extreme oversimplification.

Error above the loop bandwidth shows up as distortion. To use a PLL to
recover FM, you use a wide bandwidth that covers the entire baseband
spectrum of interest. That way, the error *is* the signal. Very
standard technique.

-- jm

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