I don't know how to solve the mobile phone number in iPhone id double authentication.

The use steps of Apple's dual authentication for iOS are as follows: 1. Log in the Apple ID and password on a new device or browser. Take iCloud in the iOS system as an example: the system pops up a dialog box of double authentication. If the user's Apple ID has been logged into two or more iOS devices or macOS devices, and the device system version meets the conditions of using double authentication, the other device will receive the Apple ID login request and login location (the location often shows abnormality in Chinese mainland after the test, so it is recommended to ignore the login location directly if the operation source is confirmed), and the system will automatically generate a 6-digit verification code after clicking Allow; 2. Enter the verification code just obtained on the new iOS device to complete the double authentication of the Apple ID; 3. If you don't have a trusted device at hand, you can click "No Verification Code Received" and choose to send the verification code to a trusted mobile phone number. The verification code will be provided by SMS or telephone. 4. If you can't automatically receive the verification code on the trusted device, you can also get it through "Settings", and offline devices can also use it. A) go to settings > iCloud, and tap the user name that has logged in to the Apple ID. If the current device is online, click password and security > get verification code; B) If the device is offline, click to get the verification code.