We do most of our communicating via phones on platforms that encourage flip, nuance-free takes, are hotbeds of disinformation, and so on. Nothing about the environments we exist in foster positive, meaningful communication that collectively benefits us. Everything we used is designed to divide.
Our inability to collectively get along ramped up exponentially as smartphones took off. Phones, and the platforms within that people have become dependent upon, are the root.
Edit: Instead of getting to know people at a deep level, understanding what shapes their core views and how they view the world, and constructively communicating with them to shape their worldview over time for the better, we prefer to yell and scream at each other in 140 characters for the sake of upvotes.
Real change and progress takes time and effort, but for some reason we're collectively deluded into thinking that it'll happen via upvotes in 45 seconds and without ever having looked one another in the eye.
Computers, whether phones or otherwise, may be a catalyst, but I am not convinced they are the root cause of our inability to get along.