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From skepticism to sustainability: changing perceptions of refurbished phones
(www.techradar.com)
Tip 1: Fairphones,Iphones,Pixels and Samsung phones are the best for long term software support.
Tip 2: Opt for a phone brand that is repairable and has a unlockable bootloader.
Tip 3: Install linux on your phone to keep getting software support.
Sorry for speculations (anyone wishing to share the statistics/data?), but i strongly suspect, most phones are discarded after they are physically damaged (think: broken screen), stop receiving support or due to the perceived need for more storage (for selfies and cat videos).
I don't believe "worn out flash chips" is a massive problem. First time i see it being mentioned, actually. ๐