I think they use the virtual line when it gets very busy, or during covid when they were severely limiting capacity inside. I've done it both ways. They have a QR code posted outside the shop when it is being used.
Pro tip if they are using the virtual line: we signed up and it said 15 parties ahead of us. The "standby line" on the side of the entrance was long. We hung around a couple minutes because my husband wanted to ask the CM managing the line a question. She alerted a bunch of people in the virtual line and no one showed up, so we got in almost right away as opposed to the standby people.
PHXscuba