Considering that the SE is a cross between the iPhone 6 generation's more powerful hardware and the form and the 4-inch screen size of the older 5S, it serves as an ideal middle-ground. The SE, the iPhone 5, and the 5S are the smallest phones on the list. Per ASCI's report, "Apparently, consumers were craving a new iteration of a smaller, less expensive phone as the SE is Apple’s first update to a 4-inch phone since 2013."
The ASCI's numbers are based on interviews it conducted with about 180,000 American consumers, reporting on annual trends and data from more than 300 companies in dozens of different industries. It ranks all of its lists on a 0-100 scale and, for this report, based its findings on 36,194 interviews conducted between May 2016 and April 2017.
Here's the full rundown of brands and models included on the customer satisfaction list for smartphones. You can read the full report here.