It would set a higher bar for a bot, but SMS wouldn’t stop them.
There are SMS providers that will happily spin you up a number with one API call, then return any messages sent to them.
The spam account could have a number, confirm the message, then delete the account faster than a human could solve a captcha.
In most of the places I exist, I think of them like janitors. Doing appreciated, but not-very-fun work, to keep communities moving.
Honestly, if I was in a place with moderators that felt like adversaries, I might not stick around very long.