Cannot Search Outlook Contacts
In order for Skype for Business to search your Outlook Contacts, Outlook needs to be running in Cached mode.
If your Outlook Client says "Online with: Microsoft Exchange" this is non-cached mode.
If you Outlook Client says "Connected to: Microsoft Exchange" this is cached mode.
More information can be found here: https://support.office.com/en-in/article/Turn-on-or-off-Cached-Exchange-Mode-78c1b9a7-9677-4655-ab97-d20ca35e29f9