One of our pilot users recently ran into an issue where she was only getting one way audio during Skype calls. She could hear the caller, but they couldn’t hear her.
Digging a little deeper, I noticed that there were no apps listed within General > Privacy > Microphone
Turns out that the user had at one time enabled restrictions on the device (she has kids). One of these restrictions was to disable access to the microphone
Resolution
To resolve this, I turned on allow changes and ensured the tick was turned on for Skype for Business.
After doing so and re-launching Skype for Business, the app prompted to be given access to the Microphone.
Voila! 2-way audio restored.