Explain to me the difference constitutionally between driving intoxicated, which is against the law in all 50 states, and driving while texting or talking on a cell phone.
Why should one law be constitutionally legal but not the other? In both cases they can cause you to possibly lose control of a vehicle that can the kill people around you, yet you seem to see no correlation between both being impaired acts at all.
I have seen people driving erratically all the time, and 5 will get you 10 there is a phone stuck to their ear while it happens.
Your question really doesn’t make sense when it asks for a constitutional difference between conduct by the citizens.
The Constitution is a definition of the structure that government takes once the source of its power (the citizens) has been declared. The amendments to the Constitution make clear that regardless of its structure, there are certain things that the government cannot do. One of those things is to seize a citizen without a really good reason. I think it is unreasonable to seize every person with a cell phone in a car just because you don’t like the way some of them drive. Anectdotal evidence is not a reasonable basis for criminalizing behavior.