Apple Watch Cellular vs. GPS: Minimum iPhone requirements
Source: Christine Romero-Chan / iMore
Both the Cellular and GPS versions of Apple Watch Series 4, Apple Watch Series 5, Apple Watch Series 6, and Apple Watch SE require at least an iPhone 6s running iOS 14. If you use Family Setup with a GPS + Cellular Apple Watch, the iPhone is only required for the initial setup. After that, the person set as a family member does not also need an iPhone.
Apple Watch Series 3
As of September 2020, Apple no longer sells the GPS + Cellular version of the Apple Watch Series 3. We no longer include its specifications in this comparison guide. However, the Series 3 GPS + Cellular does exist in the world for those considering upgrading from this model.