Grey Templar wrote:phoenix guard are good at what they do.
now, they do NOT kill things.
their job is to take a charge and hold the enemy in place while you flank them because they are good at surviving with their 4+ armor and Ward save.
Flaming attacks are just a side benifit.
use Phoenix Guard to form the center line and pin elite enemy units. then flank those units with Swordmasters or White Lions.
Pretty much this.
They are NOT destructive units. These guys are intended as a solid defensive/anvil block that can generally stand through attrition, and in an army of (relatively expensive) T3, low armor troops, that solid 4+ Ward Save is VERY appreciated. Though note: They don't come with Flaming Attacks naturally, though lots of people seem to enjoy giving them the Banner of Eternal Flame these days.
Depending on your playstyle or preferences, they're not absolutely necessary or anything, but they're certainly worthwhile if you need a solid anvil unit.