Hopefully I won’t need to for a long time!
Judging from this thread, most people replace their android phones if they break them or they start running out of space or if they start slowing down, or most commonly, if they start having to be rebooted too often. The latter is how all my older android phones bit the dust eventually. I just got tired of having to reboot them all the time, and the reboot times get longer and longer too, exacerbating the problem.
This time I’ve been trying to get around that by installing almost no apps on my Nexus 6p. Every other useful app I still install on my old Oneplus One. Audiobooks? 1+1. Listening to music? 1+1. Fandango, Mint, Google Newstand, NPR news app, MyFitnessPal, CardioTrainer, Redbox, Kodi, Steam app, Amazon Music, Games, etc, I try to limit to only my old 1+1. My Nexus 6p only has my Google apps, Kindle app, my ESPN fantasy football app, and my credit card/banking apps, and Whatsapp. I’m hoping this means that the phone will last a lot longer than most Android phones have lasted for me in the past.