In Phaser 2 when working with sprites it is possible to use a mask to make only a portion of the sprite visible. This can come in handy for effects that are like that of a spotlight where only a certain area of a sprite is visible that falls inside that of a mask.
In this post I was using phaser 2.11.1 for the code examples. So if you run into problems reproducing the code on your end be sure to check the version number of phaser that you are using. The code will break on newer major releases of phaser.