It's more expensive to waterproof a phone with a removable battery. Yes, there were phones from the 2010s that were waterproof and had removable batteries, but that was a feature you had to pay extra for.
And phones are currently the most expensive they've ever been, even adjusted to inflation. Waterproofing with replacable batteries would barely dent the price, especially after a few years.
I highly doubt that they're the most expensive they've ever been. iPhones and flagship phones may well be because the companies that make them know the morons that buy them will pay $1000 for a status symbol, but you can purchase new smartphones for under $200. Considering the original iPhone cost triple that, your claim seems ludicrous.
I sell a phone for 1 billion dollars. That raises the average price to a million dollars. If you go to any store and grab 100 phones at random, their pricing will not reflect the average.
That's why the market share of premium phones increasing is especially relevant, as I said at the bottom. For instance, 45% of Apple's sales are in this sector and Apple is the most popular phome brand in the US. Even their "budget" lineup starts at $430.
None of the premium phones will face a price increase because of this regulation, this much should be obvious. And since cutting edge technology quickly becomes cheaper, after two or three generations budget phones will also have replacable batteries while being waterproof while remaining as affordable as today.
Something that isn't mentioned either, the cost of simply replacing batteries is much, much lower than purchasing an entirely new phone, for both you and the environment.
That's not relevant. People blindly paying more for status symbols does not mean phones are more expensive. It means more people are willing to spend $1500 on a status symbol. That those people comprise ~60% of the market isn't indicative of prices trending upwards, it's indicative of stupidity trending upwards.