Problem with vector shadow

I got the following made within illustrator, but i am trying to achieve the shadow effect which is on the picture to the right of the cellphone.

So far i have used the pen tool to outline where i want the shadow, and used the gradient tool with a transparent end.

However, the gradient starts at the top left, and then the gradient effect doens't work.

How do i achieve the effect on the picture to the right, within illustrator?