Protectionism only works when two things are true: - Other countries can't produce the product better than your country can - Other countries can't sell the product to markets besides yours

If we were to enact a tariff on foreign-made smartphones that was so high that they couldn't compete with domestically-made smartphones, the smartphone manufacturers in China and the rest of the far east would just sell their phones across the rest of the world, where they would out-compete our phones on price (initially). Our domestic manufacturers would have a smaller market and less access to materials and technical advancements, causing our phones to become inferior in quality as well as overpriced. And that would eventually hurt our people and our entire economy as well, because we won't be able to enjoy the technological advancements and lower-cost goods that the rest of the world is benefiting from.

The Soviet Union used to have a pretty self-contained, very protectionist economy, and the low-quality of their goods was a standing joke in the US for decades. That's what protectionism gets you if you're not the sole manufacturer or sole market for a product.