Office 365 E1, Business Premium and Essentials licenses only provide Skype for Business Basic client, which does not include Voicemail or Call-Forwarding features.
If you have Business Premium please see our article Business Premium users: https://support.via.co.uk/hc/en-us/articles/360034764732-Skype-for-Business-Installation-for-Business-Premium-Users
If you have an Office 365 E1 or Essentials license follow these steps to install Skype for Business Full
1) Download Lync 2013 from here
2) Install the MSI once downloaded.
3) Go to Windows Update page and select Advanced Options, ensure that Give me updates for other Microsoft Products when I update Windows is selected.
4) Check for Windows updates and install these to update Lync 2013 to Skype for Business 2015.