Ran into this today logging into PayPal (the password-must-be-8-20-characters payment service) for the first time in a long time to buy a band t-shirt. After jumping through two different types of CAPTCHAs, now they require you share your phone number to log in. I contacted support via Twitter saying they have my email if they want to verify a login because I'm not comfortable with SIM jacking nor how data-mining is cross-referencing phone numbers (I can set up U2F or TOTP after initial verification). They said call them... which is still giving out your phone. I tried to use a Google Voice number, but I got an error about these types of numbers being blocked. To get a non-useless level of support, you must log in so it's either give up your data or no service for you. You shouldn't be required to give out your number to most online services.
I just feel bad for the indie band I couldn't support.