Open Settings, You, Sign-in and security.
Two-factor authentication
Choose your country code, enter a mobile number and then the 6-digit code sent by text message to finish enrollment. After that, sign-in asks for a code sent to that phone. The number is separate from your profile's contact phone. The app uses text codes only, with no authenticator keys or backup codes, so keep access to the enrolled phone and never share a code. Standard message rates may apply.
Credentials
The same page changes your sign-in email, password and the sign-in methods you use. Email and password changes ask you to sign in again. A new email takes effect after you follow its verification link, and a new password must meet the rules shown in the form. A phone sign-in account changes its sign-in number with a text code. Editing the contact phone in Profile changes none of this.