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Phone numbers cost $1 to bypass this.

Notice that he wrote "features". That's plural, meaning more than one. And then notice that he wrote "such as validating phone numbers". The "such as" part indicates that phone number validation is just one example among several. I'm sure he's quite well aware that phone numbers alone are insufficient. That's why they would likely be combined with other approaches.

I'm uncertain why pointing out the mentioned feature is easily bypassed is irrelevant?

It isn't like I was attacking him on it, just pointing out that feature is effectively ineffective except against truly mass bot type stuff.

Phone numbers are a dime a dozen these days..you need more like SSN validation.

Is there any way to delete recommendations? E.g. delete your account?

If so, you may end up with people deleting their account if they have bad predictions (the usual survival bias of mutual fund investments).

A solution would be to never delete postings, just maybe changing the username into [deleted123] or so.