Phelios consists of seven chapters, and in each, you must defeat Typhon's minions using your sword which can emit fireballs at them. However, holding the fire button down for a few seconds will charge the sword; and upon releasing it, it shoots a larger fireball that does a fair amount of damage. During the game, you collect items that increases your speed and give you more firepower.
At the end of each chapter, you have to destroy a boss in order to proceed to the next one. Between each chapter, you can watch an intermission that details what is happening at the temple.