Fine, I looked in my box of cables and found two perfect cables: yellow-white-red RCA on one end and 3.5mm TRRS plug on the other

Finally, after many hours found a "Phono Port FAQ" on the Vizio site where they recommend one adapter cable on Amazon which you apparently HAVE to use with your composite cable to mate properly with the way Vizio wired the "phono port".Here's the problem

And Vizio doesn't document the required pinouts - neither does the magic adapter cable from Amazon that actually works

Do yourself a favor and get that magic cable from Amazon before you buy this TV if you need the composite cable hookup