Based on my interactions with teachers, the administrative class that runs these schools are cowards who don’t want to deal with angry parents, nor the liability if the phones get confiscated and then stolen/damaged. There’s also a lot of parents who want to text their kids during the school day and get mad when they can’t. A lot of teachers have given up since the higher ups won’t back them up. This happened around 2015 or so, when smartphones became ubiquitous.