How are basement levels in shopping malls designated?

There are, unfortunately, no North American standards for floor numbering in commercial buildings. P1 / P2 are common if it's a parking level and are spoken just like that (they can also be 8 floors above ground). "Basement" in a shopping mall will probably be avoided, as it implies that's where the cheap goods, rejects, maintenance facilities and extra stock are put. I have seen "Lower" used in place of Basement once or twice: "Did you look on L2?"

This is a reasonable question without a similarly reasonable answer, because, at least in the US, these are influenced by regional custom and sometimes company practices. I've seen the designations of levels change when a shopping center was sold by one company to another. That said, most commonly, if the level containing the food court is "B1", the full way to say it is

The food court is on level B1.