Who would be at fault if you stopped at a stop sign looked both ways proceeded to cross and you were hit by a speeding motorist on a cell phone?

The motorist is clearly at fault; automobiles must ALWAYS yield to pedestrians, in any case. The previous response assumed you were on foot. I'll assume were in a vehicle. When you looked both ways, you should have estimated the speed of any approaching vehicle and remained at the stop sign until there was an opening large enough to cross safely. It's going to be a lot harder for you to prove he was speeding than it will be for him to prove you did not yield right of way at a stop sign.