I personally am fine with this.
how would they track you?
The reason they want a phone number is, that it’s a relatively cheap way to ensure people not signing up bots galore, as getting phone numbers en masse is a lot harder than getting email accounts
phone numbers are typically tied to your name/identity, and phone companies can locate you using their towers and such. Giving a company your phone number is identical to giving a company your full legal name and address.
yeah, no idea why you’re getting downvoted, it’s clear why companies are so eagerly embracing and requiring 2FA – if the benefits were only for the consumers, it wouldn’t be mandated anywhere near this quickly. but when they know they get a real human phone tied to every account, that’s a huge motivation