Hi SatelliteMike
Based on my test, the user-defined fields cannot be visible in the .csv files. Therefore, to share the contacts with the user-defined fields to other users in your organization, please try these 2 ways:
1. In the “Contacts” page of Outlook, right-click on the “Contacts” which you want to share in the left panel and select “Share” -> “Share Contacts”. Then select the recipients in your organization whom you want to share the contacts to, once they receive the emails, they will be able to view the contacts with the user-defined fields by clicking “Open this Contacts folder”.
2. Export the contacts with the user-defined fields to a .pst file (instead of a .csv file) and then let the users who want to view the shared contacts import the .pst file to their accounts using Outlook.
Thanks,
Allen Zhang