Determining the cell phone number of a site visitor, is it legal, does it cause negative?

Question

Marketing

And what are the driving stones of this?
Here they sent a presentation of the service, and there everything is described as legal.

Answer 1

So that such marketers and collectors burn in hell, creatures ...
Here's Itshnik's assessment for you as an ordinary user.
Fortunately, there are browsers on the bodies that block this garbage

Answer 2

Yes, because the user himself agrees to the terms of cookies on the site.
Negativity is likely to cause, but try to let less people know about what you use :)

Answer 3

This is not a toaster question. This is a research question. At least through some Yandex.view / cleanup.