sounds like they are more interested in keeping bots out than verifying identity
I believe Discord can afford to ignore those 3 people. Not saying it's convenient for the user, but it's not enough of an issue to encourage Discord to find a solution.
An effective verification system usually involves money at the root; verification in the style of phone verification works using proof of ownership of a limited resource, and most limited resources cost money (phone numbers, IPv4 addresses, etc).
In the real world this is analogous to charging money for access to an event purely in order to ensure it's not overrun with attendees,improving the experience for people who care enough to pay to get in. There are similar downsides to this; people who don't have money are left out.