Collision detection not working in Phaser 3

I am new to phaser. So I started working on a game but I am stuck at implementing collision detection. I want to do it between a static group(dot) and a Sprite(obs).

function create(){


dot = this.physics.add.staticGroup(dotx, doty, 'dot');  

dot.create(dotx, doty, 'dot');

obs = this.physics.add.sprite(obsX, obsY, 'obs');

this.physics.add.collider(obs, ball, alert, null, this);

}