If your microphone is not picking up the sound when making the call, please try the followings.
When you pick up the call with iOS, sometime you need to select Vie Fit as the microphone otherwise the mic is connected to the phone mic. Please check the setting
When you pair the earphone, please make sure you have paired as the media and phone call as well.
If your voice is too low when you are making the call,,
Vie Fit uses Qualcomm's 8th generation noise canceling technology. It recognizes your voice and enhances while suppressing the outside noize. It works well unless the outside noise is too loud or the voice is too low. In that case, we recommend to move to the place quieter or to raise your voice louder.
Note) May, 2018
Based on the feedback that the mic volume is too low, we are addressing this issue to raise the volume with the future firmware update.