Okay, let's try to understand "conceptual necessity." Imagine that you have a shape like a triangle. A triangle has three sides and three angles. You cannot have a triangle without those three sides and angles. They are necessary for it to be called a triangle. This is what we call "conceptual necessity." It means that something has to meet specific requirements or concepts to exist or be called by its name.
For example, you cannot have a cat without it having fur, four legs, and a tail. Those things are conceptually necessary for something to be called a cat. In the same vein, you cannot have a number without it being associated with a quantity. For example, if you have five cookies, the number five is conceptually necessary to represent the number of cookies you have.
So, in short, conceptual necessity means that something has to satisfy particular concepts or conditions to exist or be called by its name. These concepts or conditions are essential for it to be what it is.