how far does the phone need to be rom watch to sync

Hi

Normal Bluetooth range is around 33 feet / 10 meters. The actual range will vary in practice due to wireless interference, but you don't necessarily need to have your iPhone on or immediately around you (within arm's reach, for example) for the devices to maintain their Bluetooth connection.

Your watch can also perform certain functions when it is not connected to your iPhone, including some that are available when your watch is connected to a known Wi-Fi network.

When the paired iPhone is not within range and your watch is not connected to Wi-Fi, you can still:

• Play music from a synced playlist on your watch.
• Use the watch to tell the time, along with alarms, timers and the stopwatch.
• Keep track of your activity (Stand, Move, Exercise) with the Activity app.
• Track workouts with the Workout app.
• Display photos from the synced photo album.
• Use Apple Pay to make purchases.

If your watch is disconnected from your iPhone, but within range of a (2.4GHz) Wi-Fi network that your iPhone has connected to before, the watch can connect to that network and you can also still:

• Send and receive messages using iMessage.
• Send and receive Digital Touch messages.
• Use Siri.
• Make and receive phone calls if you have Wi-Fi calling enabled (depending on your carrier).

For the best performance from your devices, keep both Bluetooth and Wi-Fi permanently enabled on your iPhone. Should they become disconnected, your watch and iPhone should reconnect automatically via Bluetooth shortly after being brought back within range of each other.

More information:

Use Apple Watch without its paired iPhone - Apple Support