Why don't you read the study and raise the specific confounders you think are missing?

The answer is universally "no", there's no such thing as "controlling for [all] confounding variables" without blinded randomization. But we unfortunately have to rely on observational studies to try to understand the world. At least to understand what specific questions can justify the cost and complexity of a randomized study.

So yeah, of course there are confounders. Some are controlled in this study and others are not. Which are the important ones you think are missing?

> and if kid has phone it doesn't read (books)

I haven't read a physical book in about a decade. I read everyday. How is this possible?

> Obviously reading improves reading and if kid has phone it doesn't read (books), but plays games or watch videos.

We've been wrong about "obvious" things many many times before. And even in this article they refer to some evidence that hints in the opposite direction as this "obvious" mechanism.

> One showed that texting benefits the skill of grasping meaning; the other showed texting to be a negative influence on basic reading mechanics at the letter and word level.

(FWIW, I largely agree with you that this is obvious, but we should try to build our knowledge from the basics regardless)