also if you actually care about minimizing environmental impact of your smartphone purchases… either buy a new current version iPhone and run it into the ground (complete with multiple battery replacements over its lifetime), or buy a used iPhone and run it into the ground.

if you can’t stand iOS (I can’t), then you’re at an environmental disadvantage, but… make sure the OS update lifecycle is long - iPhones have a ~5 year lifecycle, and AFAIK the closest you’ll get in Android land is that Google and Samsung have a 4 year update lifecycle - and buy something that’s a flagship or close to it (like, a current Snapdragon 7xx or similar upper-mid-range SoC is probably fine, but even a Snapdragon 6xx or similar mid-range SoC means you’re gonna shorten the phone’s lifespan a lot).

definitely don’t buy low-end phones - the fastest bottom-end phones of 2020 are on par with the iPhone 5 from 2012 and the Galaxy S4 from 2013 on single-threaded performance, the fastest low-but-not-bottom-end phones of 2020 are on par with the iPhone 6 from 2014 and the Galaxy S7 from 2016 on single-threaded performance.

and why did I say iPhones at the start? iOS devices will have a longer relevant performance lifetime than Android devices - even among flagships, Android devices lag 2-3 years behind on single-threaded performance (and in fact, 2020 saw no increase in Android single-threaded performance over 2019), and that’s 2-3 years sooner that bloated software causes you to want to replace your phone. (iOS users complain about their devices getting slow after a couple years, but in Android world, the devices start out as slow as a 2-3 year old iPhone.)