Downloading the directly from Outlook 2016 to Excel is not a native one-click feature. To accomplish this, you must first transition the entries into your personal contacts or a temporary contact group before exporting them to a spreadsheet-compatible format like CSV. Method 1: Exporting via "Add to Contacts" (Simplest)
This method is best if you need a permanent local copy of the GAL in your Outlook contacts, which you can then export to Excel anytime. How to export offline Global Address List from Outlook? how to download global address book in outlook 2016 to excel