Skype for Business is used for collaboration. One can conduct meetings, hold video conferences and so on. But sometimes if you are travelling , it might not be always possible to attend a video conference. In this case Skype for Business has a facility where you can dial in and join the conference. You would be able to hear the audio and also participate in the conference.
You don’t need to download an app or have a data connection to use this facility. All you need is phone, the number to dial and the conference ID.