Banks always offer multiple choices. Always.
Let's say that Truth Social decided to go with an email verification option.
Anybody can create a hundred personal email addresses for free and use them to create a hundred accounts on the same platform.
It's much more difficult (and much more expensive) to have one hundred unique cell phone numbers to create a hundred accounts on Truth Social to create mischief.
Truth Social needs to be more careful than the Big Tech/Deep State controlled platforms like Twitter and Facebook as they have many enemies out to destroy them and do whatever they can to prevent Truth Social from getting off the ground. As it poses a real threat to their monopoly on the masses.
So I don't blame Truth Social for taking extra steps to avoid millions of bot accounts flooding the network to cause trouble.