How old are you? Small phones with replacement batteries have always existed. Batteries being removable has nothing to do with size, that's industry propaganda.
If anything, phones have gotten BIGGER as batteries became non-removable. But that's just because people buy big phones more.
MOST flagship Android phones 10 years ago were small and had removable batteries. The Galaxy S5 was the last flagship from Samsung to do it, to name one.
They've always been bigger. You show me a phone with a removable battery and I'll show you a phone that's smaller with similar features from a close time period. Might even be ip68 to boot.
Your logic is flawed. Phones have only gotten BIGGER as removable batteries have been phased out. Nearly every phone today is huge, and hardly any have removable batteries.
The Galaxy S series had removable batteries until the S6 dropped the feature. And the S5 was IP67 rated. Small, waterproof phones with big, removable batteries are entirely possible. You're just falling for the propaganda.