Work iPhone: Forgotten Apple ID password & phone number
I have a new iPhone issued by my employer but have forgotten the password for my work Apple ID and the phone number of previous phone I used it on.
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Your employer would usually provide you with a managed account, and they can reset passwords.
Create or reset user passwords in Apple Business Manager - Apple Support
Contact your IT group.
If your employer (somewhat unusually) did not, create a new Apple Account and use that.