Doing a full zero to 100% of charge on my iPhone

Batteries - Maximizing Performance - Apple

No, that is not true and never has been true with lithium batteries. And deep cycle discharges hasten the decay of lithium cells so it is best to avoid them. That urban-myth for lithium batteries persists as a carry over from older battery types such as nickel metal-hydride (NiMH) chemistry.

Apple used to recommend period full discharges and charges to calibrate the battery meter display - but it was never a good idea in terms of battery health. The current battery meter displays are self calibrating and need no such maintenance.