I highly discourage replacing text with a spinner, because that would mean you remove the call-to-action description. Don't ever remove important information from the eyes of the user just because you are working on something! That's bad UX.
Also do not freeze the whole screen if not necessary. Keep the UI usable at all times. Maybe the user doesn't even care about your async operations and just want to carry on... Forcing them to wait would be a bad decision, if it is not needed for the process they are currently working on.
Important: Put a spinner someplace, so the user can see that the application is working. If it is before the text or after doesn't really matter, you should decide based on your design.