Give the game a minute or two to load up, then click on the video game area itself to activate it and then insert a coin. Have Phun!
PHOENIX :: Classic Arcade Phun :: courtesy Iron Feather Journal #18

CLICK GAME FIELD TO ACTIVATE

1 = Player Start
2 = Player Start
3 = Insert Coin
Left Arrow
Right Arrow
Down Arrow or B = Shield
SPACE = Fire