Interpersonal interaction, face time, people belly to belly. Gregarious people are those that interact socially more.
As TV rose, it very slowly degraded social intercourse. The rise of the internet made it worse.
Cell phones show it might be something that can just be prevented. AR is just coming on the scene, and VR is at it's heels.
It's difficult to even imagine people are going to interact more in person as our phones replace our friends and neighbors.
"...I still dont think its safe to say that this is due to cellphone usage."
Have a look at the charts on the link I pasted. It's pretty obvious. If you read the article, it discusses how phones keep us apart, and how that impacts our kids.
It's not a positive influence.