If a company provides your phone, then it has access to it, and if you don't want your company to have access to what you do on it, you use a different phone. If you want the convenience of a personal phone that you can check your work mail (or work facebook groups) on, then you grant access to that company.
Right, and as I said in another comment, my statement here isn't to suggest I don't know what a burner phone is. My statement above is because I'd think someone would either say "We use our personal phones" or something similar to describe how they talk about FB without FB knowing it.
Describing your personal phone as a "burner phone" seems odd and possibly telling that there's something else there.
There very well might NOT be, but as I mentioned before: the article doesn't really say much further so it's hard to know.