Lync 2013 re-branded as Skype for Business in Windows Phone Store
When invited to a business meeting being disseminated through Skype for Business, you do not need to be a member to take part in the conference. However, if you want to use all of the features and initiate a meeting, you do have to be a Skype for Business account holder. Microsoft says that the app is more intutitive and secure, even including at-rest data encryption to protect your conversation history and voicemail. If you have the latest server software, all conversations will be sync'd across your phone, tablet and PC.
Those running a Windows Phone 8.1 powered handset with Lync 2013 already installed, will be automatically updated to Skype for Business. Those using Windows Phone 8.0 are being told to continue using Lync 2013 or Lync 2010.
Download Skype for Business (Windows Phone 8.1) here.
source: Microsoft via WMPoweruser