It would be nice to have a better fix on the historical location of the smartphone vis a vis obsessive, anxious use, but my reading of folks like Johann Hari and Tristan Harris puts it around 2013/15, which tallies with my observations in London.
That was already there in 2010. There was a Cambrian explosion of apps in 2008/2009, and Apple ran the “there’s an app for that” campaign in 2009/2010. Facebook was there on day one and there were multiple Twitter clients. Instagram launched as a picture-focused, iPhone-only social network in late 2010.
The Nexus 4 was the first Android device which was generally usable, it came out in 2012. Everything before it was a heavy compromise. And while the iPhone was usable before that time, the price of it didn't really make it accessible.
Not GP, but my personal requirements for "generally usable" include the device being able to make calls and connect to Wi-Fi without freezing for two minutes. My first smart phone was a mid-range device bought around 2011, and enduring it for 2+ years successfully convinced me to never again buy any smartphone but the most recent flagship. I don't know how people can stand living with phones that are barely powerful enough to lift their own OS. This must be bad for one's mental health.
The first iPhone was released in 2007. You could argue that ”modern“ smartphones took a few more years, but definitely not until 2016.