Comment by ejj28

Any alternative would have to be inconvenient by design in order to work though, that's why phone numbers are used in the first place.

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.