Particles.Arcade.Emitter#physicsSortDirection

If this Group contains Arcade Physics Sprites you can set a custom sort direction via this property.

It should be set to one of the Phaser.Physics.Arcade sort direction constants:

Phaser.Physics.Arcade.SORT_NONE
Phaser.Physics.Arcade.LEFT_RIGHT
Phaser.Physics.Arcade.RIGHT_LEFT
Phaser.Physics.Arcade.TOP_BOTTOM
Phaser.Physics.Arcade.BOTTOM_TOP

If set to null the Group will use whatever Phaser.Physics.Arcade.sortDirection is set to. This is the default behavior.