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, Samsung Gear/Galaxy Watch (running Tizen OS) and Android Wear OS watches.
Can I use Apple Watch without iPhone?
Can I use my Samsung watch in standalone mode, without the phone?
Can I use my GPS-equipped Wear OS watch without a phone (in Standalone mode)?