Legal Question in Entertainment Law in California

Re: copywritten

The 6 word phrase would have to be truly "original" to be protected by copyright.

More likely, the phrase could be a trademark for the product... but only after it's been used as such by the manufacturer.

What you probably want to do is ensure that the phrase is kept secret (A Trade Secret), and only disclose it to the company under circumstances that would assure you get paid if they adopt and use it for their advertising. This is typically called a nondisclosure and noncircumvention agreement.