What I'm asking is, how is this unique to self-hosting? You set them up on Cloud Email and it asks for a phone number to create an account, then they find out

What I'm asking is, how is this unique to self-hosting? You set them up on Cloud Email and it asks for a phone number to create an account, then they find out some debtor used to have their phone number and they're getting calls from debt collectors, or they move and want a number in their new area code, so their phone number changes. No one thinks to update it with the email provider until they insist on sending a code to the phone number you used to sign up ten years ago. Or you set it up for them and it prompts for a backup email, which they don't have because the one being created is their only one, so you use yours thinking something is better than nothing, and now they still need the code sent to yours. How does the hosting method affect any of this?