The Atlantic has a very thought-provoking essay that suggests they may be.
The more I pored over yearly surveys of teen attitudes and behaviors, and the more I talked with young people like Athena, the clearer it became that theirs is a generation shaped by the smartphone and by the concomitant rise of social media. I call them iGen. Born between 1995 and 2012, members of this generation are growing up with smartphones, have an Instagram account before they start high school, and do not remember a time before the internet. The Millennials grew up with the web as well, but it wasn’t ever-present in their lives, at hand at all times, day and night. iGen’s oldest members were early adolescents when the iPhone was introduced, in 2007, and high-school students when the iPad entered the scene, in 2010. A 2017 survey of more than 5,000 American teens found that three out of four owned an iPhone.
The advent of the smartphone and its cousin the tablet was followed quickly by hand-wringing about the deleterious effects of “screen time.” But the impact of these devices has not been fully appreciated, and goes far beyond the usual concerns about curtailed attention spans. The arrival of the smartphone has radically changed every aspect of teenagers’ lives, from the nature of their social interactions to their mental health. These changes have affected young people in every corner of the nation and in every type of household. The trends appear among teens poor and rich; of every ethnic background; in cities, suburbs, and small towns. Where there are cell towers, there are teens living their lives on their smartphone.
. . .
Psychologically ... they are more vulnerable than Millennials were: Rates of teen depression and suicide have skyrocketed since 2011. It’s not an exaggeration to describe iGen as being on the brink of the worst mental-health crisis in decades. Much of this deterioration can be traced to their phones.
Even when a seismic event—a war, a technological leap, a free concert in the mud—plays an outsize role in shaping a group of young people, no single factor ever defines a generation. Parenting styles continue to change, as do school curricula and culture, and these things matter. But the twin rise of the smartphone and social media has caused an earthquake of a magnitude we’ve not seen in a very long time, if ever. There is compelling evidence that the devices we’ve placed in young people’s hands are having profound effects on their lives—and making them seriously unhappy.
There's more at the link.
The author, Prof. Twenge, has also written a book on the subject, going into greater detail.
I hadn't noticed this teenage preoccupation, apart from observing that when they walk around, all too often it's with their heads bowed over a smartphone - causing them to walk out into the street without checking for oncoming traffic, leading to some pretty hair-raising near-misses. However, the author of the essay thinks the problem goes much deeper than that, affecting self-image, relationships, and the whole process of growing up (possibly very negatively). I suppose the jury's still out on whether or not she's right, but she advances some pretty persuasive evidence for her argument.
Food for thought . . . particularly if you're the parent of a teenager. Is it time to confiscate their smartphones, and/or forbid them from getting or using one except during strictly limited hours of the day? Is that even possible any more?