Microsoft has released the new Skype for Business app for Windows Phone.
If you have already installed Lync 2013 Mobile client app for Windows Phone, this has been automatically (or should be) updated.
If not, try to force to update your installed app or download it from the Store https://www.windowsphone.com/en-us/store/app/skype-for-business/d85d8a57-0f61-4ff3-a0f4-444e131d8491
As part of the improvements:
- off course the same UI than Skype for Business desktop
- More emoticons available
- At rest data encryption, meaning IM conversation and voicemail are encrypted by default
- Conversations are synchronized across all the devices you use