If they allow the user a chance to send an appeal or out-of-band alternative method to verify then this becomes less of an issue. It's when people presume certain baselines — like a phone number — that it becomes a showstopper to community.
I have seen Discord servers that use 3rd party verification systems, but very rarely. An alternative to phone numbers would be ideal, but there will always be flaws similar to the flaws of phone verification in my opinion.
I totally get all the frustration over phone number verification but it simply is the easiest and most effective method. It's really hard and expensive to get more phone numbers while every other method is easy to get unlimited accounts. Almost every country has phone numbers tied to ID as well so you can report the worst of users to local police.
