Someone not using their warranty when they can isn’t solved by offering a longer warranty period.
Someone having a bad experience with customer support is not solved by a longer warranty period.
Product replacements because of poor product design aren’t reduced by a longer warranty period (the cost is different, but the replacements still occur).
The longer the warranty period, the more disagreement there is going to be about whether something is wear-and-tear or a manufacturing defect. A generous attitude towards replacing parts can be had, but ultimately it is still the customer who will pay because the up front cost of the device will increase.
Taking this further, having a model where you subscribe to a phone (not a specific model, but specific functionality) may work better. The contract would define the level of service/function, take into account what is acceptable wear and tear, and possibly offer an optional insurance for accidental damage not covered by default (as most customers don’t want to pay for the carelessness of others). If the failure rate of devices becomes high, there will be an incentive to replace that model with a different one (the subscription is for a device with the function of a phone, not a specific phone), as the servicing costs remain with the supplier. There’s been some discussion of such a model for example here.