I have 2 apple watches, Model 3 and model 6 (just purchased). I swim a lot and only want to use the apple 3 in the pool and exercise. Do I have to connect it to a phone to get the GPS for how far swim etc.

You can paired 2 or more Watches with an iPhone. (But only one can be active at any one time)

Nothing has changed.

Pair more than one Apple Watch

You can pair another Apple Watch in the same way you paired your first one. Bring your iPhone near your Apple Watch, wait for the Apple Watch pairing screen to appear on your iPhone, then tap Pair. Or follow these steps:

1. Open the Apple Watch app on your iPhone.
2. Tap My Watch, then tap All Watches at the top of the screen.
3. Tap Pair New Watch, then follow the onscreen instructions.

See the Apple Support article Use more than one Apple Watch with your iPhone.

To learn how to set up a watch for someone in your Family Sharing group, see Set up Apple Watch for a family member.

Quickly switch to a different Apple Watch

Your iPhone detects the paired Apple Watch you’re wearing and automatically connects to it. Just put on a different Apple Watch and raise your wrist.

You can also choose an Apple Watch manually:

1. Open the Apple Watch app on your iPhone.
2. Tap My Watch, then tap All Watches at the top of the screen.
3. Turn off Auto Switch.

To see if your Apple Watch is connected to your iPhone, touch and hold the bottom of the watch screen, swipe up to open Control Center, then look for the Connected status icon .