One fix that was mentioned in the comments that would have been easy to implement (and, frankly, bizarre it’s not implemented yet) is confirming password when performing such critical actions as removing or adding devices/telephone numbers.
This is essentially the famous xkcd "5 dollar wrench" problem https://xkcd.com/538/
Unfortunately I don't have an iPhone to check, but another comment [1] suggests that this may happen if you physically change SIMs. My brother said they didn't ask for his iCloud password, which makes sense: if they had the password then they wouldn't have needed the phishing step afterwards.
At this point I will just stop commenting on this post as it seems like either Apple already fixed this or some of the most critical information has been omitted by the author. So we are just guessing and raging for no reason.