Why do some phones depreciate faster than other? Based on evidence from reselling sites (eBay, Amazon etc.) we can observe a trend that iPhones on average depreciate far less and slower than for example Samsungs (or other phones that lose their value even faster). Now why is that?

Note that I am not talking about nominal prices (iPhones are on average more expensive than Samsungs) but the percentage change. I am also not asking as a "fanboy" - it is just an observation I made.
I think it might have something to do with how much a phone model is valued in certain markets. For example, the amount of utility you get from a certain phone model is higher than another phone - they are not perfect substitutes for each other. Hence, the discounted utility of the phone will still be higher, because the user still values it higher.

There is no strict formula that I know of for this comparison, but by simple logic, if you feel proud of having an iphone, it's demand will be high, will be more plastic, and hence, whether the phone is used or unused, it will sell at a higher price, so will depreciate lesser.

Must note, though, that the depreciation is not constant over time. It reduces much more in the beginning, and then sort of flattens out towards the tail end.