The app will open when you answer an incoming CaptionCall phone call, however, if your phone screen is locked, you will need to unlock your phone to view the captions.

If you are on an iPhone or iPad device, please tap the CaptionCall icon on your screen to unlock the phone and go to the captions:

If the incoming calls to your usual phone number are going to your usual phone app rather than the CaptionCall app, please see Why aren't my incoming calls being captioned?