If you are using Outlook for Mac setup and have an O365 account, your contacts are not stored on the server. They are saved on your computer.
To see your On My Computer folders, you can enable the option in Preferences. Select Personal Settings | General and deselect Hide On My Computer folders.
See Create contacts in Outlook for Mac and Create a contact list or distribution list in Outlook for Mac
NOTE: if you are using the "new" Mac Outlook, you are not able to create Contact Lists - you would need to use the "old" Outlook in order to do so