I can read that as applying personal phones hooked up to employer services. I think it's pretty common to force employees to consent allowing their employers to manage their device to get access to work email on it. I'd always assume that just mean they could remote wipe it, but maybe it's even worse than that.
Reading the post makes it sound like this only happens on managed devices; whether that means "owned and provided by work", "within the confines of the work profile on a BYOD devices", or both, I'm not 100% sure.
Is it common? I've only been asked to do that once, and I declined. I explained that it's my policy to never use my personal equipment for work purposes or my work equipment for personal purposes. They provided me with a work phone to use, instead.
Everywhere else I’ve worked I’ve had slack/teams/email/pagerduty whatever on my personal device without issues. It hasn’t felt realistic to ask for a dedicated work device for that.
But personally, I've always said no, because years ago someone at my workplace fat-fingered a command and wiped all iPhones hooked up to company services (including employee-owned personal devices). I've always seen it as a risk to my data if not my privacy.