Two watches

You can pair multiple watches with your iPhone, so you can wear different ones to match what you're doing and where you're going. Only one Apple Watch can be active at a time. You can pair more than one Apple Watch GPS + Cellular model, but not all carriers support multiple, active cellular plans at the same time. Contact your carrier for details. For more info, see:

Use more than one Apple Watch with your iPhone - Apple Support

I'm not sure why the article has been archived and is no longer updated by Apple.

You can pair multiple watches to a single iPhone. But not the other way around.

I marked this post to follow because I thought each Watch needed its own phone number and plan but I was not sure and didn't want to post the wrong answer.

I think that was the OP's question.

Thank you 🙏

You're welcome.