Within the Phish Creation tool, you will always see a button labelled as Save as Test Data.

This button can be ticked when all required steps within the Phish Creation section have been completed. Upon doing so, the Phish exercise will be hidden from the Phish Overview, Phish Audits and Phish Adoption reports.

For further information, see article:

If I Tick 'Save as Test Data' for a Phish, and then Untick it, Does This Apply to All User Data Targeted with the Phish?