Which phrase justifies why the theory of evolution is a theory and not a law?

"Evolution as fact and theory"; is a phrase that justifies this. Evolution does relate to natural selection, which is now, not a theory, but fact, as years of research, for example the Peppered Moth incident, when a factory producing contaminated organisms around it, making the trees black. This is when a gene found in the moth activated, and changed the color of the wings from white, with peppered black, to black; this let the peppered moth's, or I should say now, dark-colored moths, blend back into their environment, and hide from predators. This is an example of natural selection, that relates to the theory of evolution, which proves evolution fact, but we don't understand some parts of evolution, so therefore we say "Theory and Fact".