talking or texting on a cell phone whilst driving and, oblivious to the speed limit, driving at least 5-10 mph under the posted speed limit.
getting behind someone going 20 mph in a 30 mph zone and thinking that they're either stoned or old. Only to pull up beside them at a stoplight and seeing a teen-age girl (usually) busy tapping away on a glowing cell phone. She's driving so slow she must be phone stoned.
Being Stoned alone but on the phone with your friend who is also stoned.
Joe: I'm bored and alone, lets get phone stoned.
A person is so into what is on their phone (text message, Facebook, twitter, etc.) that they are oblivious to the outside world. They are very unlikely to respond when being spoken to.
Don't bother asking Jen what she wants. She's phone stoned!
You were just so phone stoned a minute ago. Did you even hear me?