There is not yet a body of research that supports either side of this argument, and there might not be, since much of the research this professor was conducting is now dead due to Trump DEI policy.
What is true, and what we know for sure, is the capitalist wants the phone and tablet in a child's hand as early as possible. Google wants Chromebooks in schools to make students dependent on their tools. Apple wants the same and are less successful at it. Meta wants a comprehensive psychological profile of the child to hyper target products and reproduce capitalist social values in the minds of children. They want to be the 3rd and most permissive parent in the home. They want your child engaging with AI so they can use it as a wedge in the privatization of education. They undoubtedly see the phone, the tablet, and the internet at large as the single most influential and powerful tool for mass production and reproduction of culture. They want to read your inbox, your text messages, your voice calls, and mine them all for every ounce of insight into their psychological operations effectiveness.
I think it is completely reasonable to be of the position that less phone/tablet access is good. Especially since it would seem media consumption at a young age backdoors capitalist ideology into kids and shapes the way they understands the world. Considering that there has been a seriously uncritical implementation of technology in education, which I think is only now starting to change, I believe parents should petition their schools to take a more critical and proactive approach to device use, and that these prohibitions are actually not enough and parents should be demanding more oversight on the topic.
I've talked in the past about the fact that students live most of their academic life inside a panopticon, and in many ways I think this primes students to be uncritical and even embrace the surveillance state that we find ourselves in now. All of these forms of technology, under capitalist control, are part of the effort to shape and steer culture. There should be demands for schools to implement digital literacy programs coupled with a reduction in technology use, not just for students, but also for staff, administration, and faculty. One that recognizes technology as a potential tool, but that also highlights it's corrupting influence.