"vocal champion" is correct and usable in written English.
You can use it to refer to someone who is a vocal advocate for a particular cause or issue. For example, "Yolanda is a vocal champion of equal rights for all."
Now he's a vocal champion for Confederate monuments.
James Hansen, NASA's former top climate scientist, is also a vocal champion of carbon taxes.
President Teddy Roosevelt, for example, was probably our country's most vocal champion of campaign finance reform.
The project was legislated for in 2011 under the auspices of its most vocal champion, Iain Duncan Smith.
Beyond the specifics of city policy, Mr. Giuliani was a vocal champion of immigrants and warned about fear-mongering.
The committee recommended that DfID become a "more vocal champion of health system strengthening on the world stage".
The experience set her on a path to becoming Britain's best-known midwife and vocal champion of natural birth.
In August, News Corporation said that Jonathan Miller, the company's chief digital officer since 2009 and a vocal champion of Hulu, would leave the company.
But the cardinal, a vocal champion of immigrant rights, remained hugely popular with Latinos here, who make up 40 percent of the four million parishioners in the archdiocese.
The landfill's most vocal champion, for instance, is John Hulett, the county's first black sheriff, now the probate judge and the county's de facto political boss.
Mr. Beshear, a vocal champion of the Affordable Care Act, said it was the first detailed assessment of the financial effect of Medicaid expansion on a state.
