I guess the question is this.

Can somebody review the objective/subjective experience of a being at a show without being there? Obviously, no.
Can someone review the quality of the music played there?(filtered through ones subjective preferences). Yes.

Why do we go see phish?
Probably several reasons but I think the main one would be the music(at least in theory)
Logic in this case indicates that a review by a non attendee can still be a valid review of the quality of the MUSIC! In fact I will echo deceasedlavy's sentiments here and say that person( non attendee) may indeed be more qualified to review the MUSIC!

In no way do I mean to nullify the myriad manifestations of wonder that being smack dab in the middle of a undulating crowd of phish fans manifests!