The documentation for the play method reads:
play(key [, ignoreIfPlaying] [, startFrame])
Plays an Animation on a Game Object that has the Animation component, such as a Sprite.
Animations are stored in the global Animation Manager and are referenced by a unique string-based key.
||string | Phaser.Animations.Animation
||The string-based key of the animation to play, as defined previously in the Animation Manager. Or an Animation instance.
||If this animation is already playing then ignore this call.
||Optionally start the animation playing from this frame index.
true in the second argument says that if this same animation specified in
key is already playing, don't interrupt it to execute the animation described in this call. If you pass
false instead, then this animation call will stop the current animation - even if it's the one specified in
key - and take over with the animation you've specified, starting at