It's not immediately obvious from the video that the forklift driver is indeed on his cellphone. However, we managed to capture an image (see the gallery below) that seems to show this and the video uploader, Bjorn Nyland, confirms this to be true too.
Gallery: Forklift Hits Model S
What strikes us as odd here is that there is so much open roadway upon which the forklift could travel, yet the distracted driver is on a path straight for the parked Tesla Model S. The forklift smashes into the rear bumper of the S and does some damage. The driver is aware of the collision, as you can see him turn his head to look back. Rather than stopping, the forklift operator hits the go pedal and flees.
The whole incident is caught by Tesla Sentry Mode, a feature that's proven to be invaluable in catching incidents such as this.
Here's an image of the damage done to the car. It's quite minor, though it would have been easily avoided had the forklift driver been paying attention.
Video description via Bjorn Nyland on YouTube:
I forgot to mention it: The forklift guy was using his phone while driving.