You have telephone numbers assigned to users in an Office 365 tenant for your organization. You now want to transfer those numbers to a different Office 365 tenant for your organization and you can't find the option to do that in the Skype for Business Online admin center.
Currently, transferring telephone numbers from one Office 365 tenant to another Office 365 tenant isn't supported. Local number porting is available only with supported service providers or carriers.
For more information about number porting in Skype for Business Online, go to the following Microsoft websites: