Ultimate hogwash. I had a 17t Phil cog that was loud as all hell. Swapped it for for a 17t EAI Deluxe after only a few days of riding and it was very quiet. Same bike, chain, chainring and chain tension.

In my experience on my own bike and bikes I've worked on, Phil cogs are loud because the teeth are too long/pointy and "hook" the inside of chain links as they pass over it instead of allowing them to roll off smoothly - as seen in the attached comparison pics of an EAI and Phil cog of the same size: