I think it depends on who (whom?) you ask. Some say 80/20 is brighter, and others say phosphor bronze is brighter. The problem is that we all hear and perceive things a little differently.
It also depends on the guitar, in part. Some just sound better with one type of string than with the other.
In my experience, phosphor bronze are a little warmer and more "three dimensional," if that makes sense. I really noticed the difference with my 000-15, which sounds rich and complex with PBs but a little brash and kind of flat with 80/20s. The difference is subtler on my Taylors, but still there.
Just my two cents. I'm sure others will weigh in with completely different pennies.