Pheonix does very little damage meaning you won't be able to defeat Emerald Weapon without the underwater materia, which would increase the damage done by aire tam storm. If you tried to use Pheonix in conjunction with KotR with the W-Summon materia, it would do less damage than two shots of KotR, dragging out the battle and would also raise the damage from aire tam storm. The reason I use that particular combo is that you can do tons of damage for free, and it keeps the damage down to where you won't get killed. If you have 6 materia on one character with 9999 HP, they will die during that fight. Air tam storm does 1111*X where X=number of materia equipped, so on a character who has 6 materia equipped, it will do 6666 damage, leaving that character with 3333 HP left. Revenge stamp can do about 4000 damage, and will kill that character. If you use Pheonix, it will not only cost more MP, but then you'll have to doublecast KotR twice again, and for that you'll probably need to use an ether, by which time Emerald Weapon can kill you. If you have 9999 HP and a reasonable defense and magic defense, you won't have to worry about dying since you'll regain HP every time you get hit with my combo.