Starcraft 2 Elite Guide - Stopping Mass Mutalisks With All 3 Races
Protoss employ the Phoenix against air units such as the Mutalisk
. The Phoenix delivers bonus damage to light units the Mutalisk being a light air unit this makes Phoenix's ideal. The Phoenix deals 20 damage to light air units with a 1.1 sec. attack speed versus the Mutalisk which deals 9 damage with 1.5 sec. attack speed. When you look at the simple math there really is no comparison. Simply produce an amount Phoenixs to go with your main army or guard your base and you're a-ok!
Starcraft 2 Elite Guide - Stopping Mass Mutalisks With All 3 Races