Depending on what you want the result to be, you could:

create one function, that handles both events:

function doAction(){
   alert('action')
}

and then reference the same function in the event listeners, of both actions:

this.enter = this.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.ENTER); 
this.enter.on('down', doAction);

// ... AND

this.input.on('pointerdown', doAction);

Update: If you want to, check what device type the app is being run, you could use the information of this.sys.game.device.os (link to documenation )