How China came to dominate the U.S. in smartphone manufacturing

China has controlled the smartphone manufacturing market for years. While some industries, like the semiconductors, are scrambling to build new factories across the U.S., tech giants like Apple and Google are not making the same effort. CNBC explores why phones are built abroad and whether production should move to America. And CNBC visits a startup, Purism, at its Carlsbad, California factory to take a look inside its smartphone manufacturing facility.