Yes and no, but I think high spec, late model iPhones are unlikely to end in landfill. Typically people who churn them once a year resell or gift them to others. And Apple provide a recycle program.
I don't think the above people are contributing to e-waste.
Let me clarify. By buying a phone every year you are adding phones to the marketplace total which otherwise wouldn’t have been present, those will be used second-hand by others (at best), who will then resell their phones, etc. At the end of that chain is a device that goes into e-waste recycling, so yes, by buying a phone every year you do contribute to that. You contribute to a kind of high-turnover thinking.