You won't be able to do a thing without some level of invasion of privacy (phone # verification would probably be the best).
We're unfortunately rapidly approaching the point where we have to make a decision A) a little invasion or B) allowing bots to roam free and spread propaganda across all major social platforms. Even if you choose path A it's up to the platform to implement it properly. See tiktok the racism and propaganda there has SKYROCKETED since being "allowed" to stay in the US (backdoor agreements to allow propaganda bots)