https://www.counterpointresearch.com/insights/us-smartphone-...
This does as well:
https://www.oberlo.com/statistics/us-smartphone-market-share
I would’ve been highly surprised if Samsung and Apple were head-to-head in the USA.
Apple has more than double the market share that Samsung does.
The EU considers any party that has more than 40% of market share to be in a dominant market position.
This isn't directly relatable to the USA, of course, but it shows that its far from "clear cut".