Does using FaceTime take up memory in your Iphone, or use up Data?

I've noticed before that when looking back to check how long I facetimed with another person, it would show like 121 MB, 67 MB or however much. I recently facetimed my boyfriend and we accidentally fell asleep, so I checked back on it right now, 8 hours later, and it says 2GB. That's a lot. Is this data I used up or is this 2GB space I took up on my iPhone?

Data. FaceTime is internet based so therefore (if used over a data connection) it would cost. Doesn't take up space on the phone.

Pretty sure it uses data.

On mine, it takes up storage every minute is about 5-10 MB's.