Smaller Bounding Box

var config = {
    type: Phaser.AUTO,
    width: 800,
    height: 600,
    parent: 'phaser-example',
    physics: {
        default: 'arcade',
        arcade: {
            debug: true
        }
    },
    scene: {
        preload: preload,
        create: create
    }
};

var game = new Phaser.Game(config);

function preload ()
{
        this.load.setBaseURL('https://cdn.phaserfiles.com/v355');
    this.load.image('atari', 'assets/sprites/atari130xe.png');
    this.load.image('mushroom', 'assets/sprites/mushroom2.png');
}

function create ()
{
    var atari = this.physics.add.image(200, 400, 'atari').setImmovable(true);

    //  In this example the new collision box is smaller than the original sprite

    //  220x104 original size, 110x52 new size, the 'true' argument means "center it on the gameobject"
    atari.setSize(110, 52, true);

    //  And this sprite will collide with it
    var mushroom1 = this.physics.add.image(700, 350, 'mushroom');
    var mushroom2 = this.physics.add.image(200, 50, 'mushroom');

    mushroom1.setVelocity(-100, 0);
    mushroom2.setVelocity(0, 100);

    this.physics.add.collider(atari, [mushroom1, mushroom2 ]);
}