People tend to hold their phones in "portrait" mode, rather than "landscape". So, width would typically refer to the second largest dimension when talking about (most) phones. Additionally, given that phones are 3d objects, interacted with in physical space, the "feeling" of width would also include the phone's thickness, to some extent.
In this context, the iPhone 6 is actually smaller than the Nexus 5, by about 20%.
