A:Answer Technically the features on Apple Watch - including calling and texting - is available when Apple Watch and iPhone are connected. They are designed to connect primarily connect via Bluetooth to each other - iPhone & Apple Watch.
You don't necessarily need to have your iPhone on or immediately around you for the devices to establish and maintain their Bluetooth connection. Normal Bluetooth range is around 33 feet / 10 meters, However this distance can vary - with other interference and unknown factors.
Whenever your watch can't connect to the iPhone via Bluetooth, it will attempt, as a fallback, to connect to a known Wi-Fi network.
When instead connected to Wi-Fi, the watch also still offers a number of features, including receiving and sending messages via iMessage. If your carrier offers Wi-Fi Calling and it is supported on your plan and enabled on your iPhone, you can also use Apple Watch to make calls and (subject to carrier support) send and receive texts.
Hope this helps, ENJOY your Apple Watch.