When thy need to access it to read information it is OK. For this the sharing is not needed.

When sharing is used, then several users can open the workbook simultaneously, the user who opened the workbook as first locks it, and when first user closes workbook, the next user can save changes (at least it was something like this until Excel2016 - now MS made changes to this feature I am not familiar with at all).

When the workbook is not shared, any number of users can open it simultaneously too, but none of users opening it as 2nd or further simply can't save it. In case only one user/a couple of users is entering new contacts, the only problem will be the workbook being locked for this contact info administrator, when someone else is looking for info at same time.

A possible solution is to have a master workbook, where contact info is entered by contact info administrator. and every non-administrator user has his/her own workbook, which reads contact info from master workbook using ODBC query, which is refreshed whenever the workbook is opened, or when the user refreshes the query at will. With this design, the Master workbook is always available for editing.