Heavier phones hit the ground with more momentum. Moreover, how many people throw away—not sell or trade in—their phones because of battery alone? Given the ease of replacing iPhone batteries, I’d guess it’s minimal.

The only thing more battery grants in scale is on the packaging and microcontroller. Compare that to the excess material, on account of folks charging their phone every day (switching from daily to every-third-day charging is unlikely a meaningful behavioural update), and you see the net waste. Particularly when heavy users can be segmented to with external battery packs. (Which don’t add the momentum tax.)

It could help. But proposing using more material use in an environmental discussion without thought to its trade-offs isn’t serious debate.