The jury is out on that, actually

Current research thinks that texting and other phone activities are using different cognitive territory than conversation with a passenger or operating the car controls. That territory may overlap with or interfere with the brain matter used in driving.

I don't believe they've reached definitive conclusions yet and there's a lot of research to do, but one example: Siri is commonly assumed to solve the problem but it probably doesn't.

Will be moot in five years anyway once automated driving takes hold, but cultural change is needed. Texting while driving needs to be looked at by teenagers like drunk driving increasingly is.