To me that would have more validity if there were any evidence that the texting and sexting had caused any decline in Cooper's care in the past. We have not seen that he neglected his son so that he could keep texting.
We do have instances of him ending phone calls so he could go pick up Cooper. That is about the only linkage to the two that we have heard that I can recall.
Did he spend too much time on his phone? It's hard to say since we have not heard that it caused problems in his marriage or job or with his community relationships. Of course sexting with minors and even other ladies is not healthy behavior when someone is married (and criminal in the instances of sexting minors) ...but we haven't heard any evidence that Leanna had made an issue of him spending too much time on the phone or that he was disciplined or reprimanded at work for failing in his job. Nor have we heard any concerns about him not paying enough attention to Cooper or neglecting him in any way.
Perhaps that is where this was all heading, but as of the time Cooper died, it doesn't seem like all the phone time was affecting major areas of his life.