If you have registered a mobile phone number or secondary email address on Office 365 for the password management system you can amend these details by signing-in to Office 365 and clicking on your initials (top right) | My account (or View Account) | Security Info.
Or going direct to https://myaccount.microsoft.com/
Log in with your University of Derby credentials then you can select Verify to amend the phone number or email address that you have registered.
You can also setup additional security verification to protect your account with Multi-Factor Authentication.
Please setup as many options as possible. Unfortunately, the office phone option is not available to students.