Sean Spicer defines 'mouthpiece' but doesn't get it quite right

Quoted in Trump Aides Address His Wiretap Claims: ‘That’s Above My Pay Grade’.  (The New York Times, 3/7/2017)

Strictly speaking, Sean, the role of the White House Press Secretary -- that's you -- is to serve as the spokesperson for the executive branch of the U.S government administration.

In general, you serve 3 constituents:

1. The President
2. White House staff
3. News organizations

Source:  Kids.gov