Apple confirmed on its support site that the 2nd generation Apple Watch Series 8, Ultra, and SE only use their GPS and no longer use the iPhone.
Apple Watch Ultra, Series 8, and SE (2nd generation) built-in GPS with Apple Watch, even when your iPhone is nearby. To extend battery life, older Apple Watch models use GPS with your iPhone, if available.
The Apple Watch has always used the iPhone’s GPS when the smartphone is nearby. It started in 2016 with the introduction of the Apple Watch Series 2 with GPS.
Despite the presence of GPS in the watch, Apple continued to use data from the iPhone to keep the Apple Watch from running out of power quickly. [Phone Arena]
Source: Iphones RU