On the flip side, it makes it difficult to spot dupe accounts or ban evasion attempts. I run a moderate-sized server and I have a suspicion that one of our members has weird conversations with himself across multiple accounts, but I have absolutely no way to verify that since I can't see any IPs or hostnames.
One could argue that we need more insight for administrators because of how "toxic" gaming communities can be.
This is true, but having a phone number requirement lowers accessibility to the server for users who either don't have a phone or aren't comfortable providing their number.
Catering to people who don't own a phone (Richard stallman and kids in Africa) is a lower priority to most mods than stopping waves of trolls and spammers.
One could argue that we need more insight for administrators because of how "toxic" gaming communities can be.