The Apple Watch 6 can easily work far away from the iPhone, from a range of 200 feet (60 meters) to 800 feet (240 meters).
In case the distance between the Watch and iPhone is more than 800 feet, you can use a wi-fi network for data transmission. This type of connection will let you use Siri, make and receive phone calls, send and receive texts, check the weather, find friends, stream music, and so much more.
If you are unable to connect your Apple Watch 6 to either wi-fi on the iPhone, you can still make use of a few apps like tracking your activities, make payments, check heart rate, ECG and blood oxygen, along with some other things.

Remember, the calling and messaging apps will only work if your Watch is connected with a cellular or wi-fi network.
What is the technology behind the connection distance between Apple Watch 6 and iPhone?
The Apple Watch series is equipped with Bluetooth 5.0. This makes it possible for the device to cover up a greater range.
You can find Bluetooth 5 in every Apple smartphone from the iPhone 8 on up to the latest iPhone 13 – it is practically a device standard now.
You can connect your Apple watch to your iPhone via both WiFi and Bluetooth. Therefore, when you’re home, you don’t have to be in Bluetooth range of your phone to access your messages and take calls. You can be anywhere in your house and still use your phone.
Read specifications of Apple Watch series 6 here.