The original iPhone cost $500 and adjusting for inflation that is about $800 today. I don't remember phones costing $300 since before the smart phone era. Even Walkman phones cost $500 in the early 2000's.
They can definitely make phones for $300 and you can buy a smartphone that is more powerful than the original iPhone for $50. It probably will be a bit slow running modern apps but it may possibly still be workable for a while.
The only difference is that now you can play graphicially intense desktop-style games, but no one really does that. And also it has some sattelite phone functionality. The cameras are also better, the battery life is better, but it all doesnt fundamentally change the way you use it. The complexity over last year's smartphone is unnessisary.
Now that everyone in the world is basicially required to use a smartphone, the only way for big smartphone to make more revenue is to sell each consumer more smartphone per smartphone.
Cameras have improved, but less than you think. Most of the improvement is in low-light, but in well lit scenes we actually sort of peaked 10 years ago. It's gotten slightly worse now, believe it nor not.
But you can't legitimately run a phone from 10 years ago, because while everything is the same, the software uses 100x as many resources. That sort of tricks people into thinking "oh it must be doing so much more!"
But... is it? Think back. Instagram 10 years ago, YouTube 10 years ago. Yeah... it's basically the same. Some argue they've regressed. I'm sure we've more than 10x the code size, but nobody sees that.
Web browsers have also gotten much more complex, but again, you won't notice it. We have a lot more fringe web APIs like webusb but like... the regular web browsing experience for 99% of tasks is identical.