So insignificant that it's one of the most valuable companies in the world on the back of those two product categories. By the way they are on top where it matters – profit and customer satisfaction.
I am not exactly sure what the market share is for iPhones, but Android is much larger. For computers, they are a tiny portion. If they cracked 10 percent I would be shocked. That is awesome they are profitable. But yes they do have an insignificant user base for computers. A reasonable but nowhere near dominating position for phones. Apple is always going to be a relatively small player regardless of market cap in the tech world. The last couple decades have proven that
Apple’s genius is focusing on profit share over market share. They make a minority of phones but capture the majority of the industry’s profits. That lets them expend more in R&D, more on top people, et cetera.
Having 19 percent of the smartphone market isn't dominating. The Samsung s8 and pixel 2 xl pretty much beat the iPhone x on most features at a lower price point. Higher ppi, battery size. And I think it doesn't even have USB c.