The phone needs to be on and GPS needs to be enabled. However, you can turn off the screen and stow the phone in your pocket or in your bag.
The standalone version is available for GPS-equipped Apple Watch and Samsung Gear/Galaxy Watch (running Tizen OS).
Can I use Apple Watch without iPhone?
Can I use my Samsung watch in standalone mode, without the phone?
Standalone support for Wear OS watches (including Samsung Galaxy Watch 4 running Wear OS 3) is coming soon.