Your iPhone has two factor verification enabled from device itself ( it's a single trusted device and verified ) and not synced with Mac or other iPhone / iPad ( the verification code can be accessed from the device when active time is inserted ) .
Whenever you try to sign in with Apple ID and password from a browser the account will not be accessed , you need to contact cellular service provider and issue a duplicate sim for the same number .
The Apple ID say example1@icloud.com exists on server and you know the password and its account credentials , however that is signed in the device iPhone .
If you don't remember the trusted number and yet it is verified in the account , visit your cellular service centre with personal identification proofs , the number can be obtained from them .
Issue a sim on behalf of the same number and insert the sim Set up cellular service on iPhone - Apple Support
In the new iPhone follow the steps in the article Turn on and set up iPhone - Apple Support
The Apple ID and password is active so is the 2FA active on the iCloud server , once a trusted number is added the code will start appearing on the same trusted number , and the person can access the account .
See the article Get a verification code and sign in with two-factor authentication - Apple Support
The mails will sync when mail box is turned on Add an email account to your iPhone, iPad, or iPod touch - Apple Support
And those mails can again be viewed View an email in Mail on iPhone - Apple Support (IN)