You could also use: public mouthpiece
Examples:
The media is a government mouthpiece, not a government watchdog.
are they the public mouthpiece for the bureau of..
The Chamber Of Commerce suddenly found it had a public mouthpiece in The Guardian as the Smedley brothers � printing press rolled out the weekly
Mouthpiece for the public sounds better than of the public in your example, (to me) and I believe it is more usual. However, I have seen mouthpiece of the government used also.