Skype for Business (previously known as Lync 2013) app today got updated to v6.3. This is a minor update with only bug fixes.
• View shared content during a meeting, on your mobile device
• Initiate a group conversation (IM or video) or invite additional participants
• Join, rejoin, and initiate a Skype for Business Meeting to communicate and collaborate amazing ideas
• Control the meeting (mute or remove attendees)
• Transfer your calls to another phone number or another contact
• Pick up your conversations from the point where you ended them last
• Join (and enjoy) a Skype for Business Meeting even if you don’t have a Skype for Business account
• Enhanced security with Skype for Business certificate and passive authentication
Download it from Windows Phone Store using the below link.