How to Make the Global Address List a Default Address Book
The Global Address List (GAL) is the central repository of contacts. Changes to the GAL are immediately available if you are using Outlook Web Access (OWA). On a regular Outlook client, however, a change might not appear for up to 24 hours. This difference is because the default configuration for an Outlook client is to use something called Cached Exchange Mode. In Cached Exchange Mode, the default is to use the Offline Address Book (OAB). Normally, the Offline Address Book is preferred because it is more responsive than the online version.
How to make the Online Global Address Book your default
Click the Address Book button. The button is located in the Find group on the far right of any Home ribbon.
In the Address Book window, click on the Tools menu and select Options.
The Addressing dialog box offers three radio button choices for your list order. The default selection is Start with Global Address List. The problem is selecting which Global Address List. You will need to add the Global Address List to the Custom list.
Click Add... and use the Add Address List selector to include Global Address List as a custom item.
Close the Add Address List dialog.
Near the bottom of the Addressing dialog is a selector labeled "When opening the address book show this address list first:" with Choose automatically set as the default.
To override the automatic selection, open the drop-down menu and select Global Address List.
At this point, it's not essential that you have the Custom list selected. It's up to you as to which address list you want to check first.
Click OK to exit the Addressing dialog.