Was told a iwatch 3 with cellular would connect to iPhone 5s without using cellular

Hi

Apple Watch Series 3 (GPS + Cellular) requires an iPhone 6 or newer model of iPhone, running the latest version of iOS 11.x

I'm afraid that it cannot be paired to or used with an iPhone 5s at all, even if you do not intend to set up or use the built-in cellular feature.

More information:

Set up your Apple Watch - Apple Support

Sorry I really don’t know. Can you get to an Apple store or talk to Apple direct. I am sure they can advise you and help you to do it if it is possible. They may exchange the watch if not. Be sure to take original receipt in case. When I was married this would have been a great excuse for a new phone.(to justify to myself not my wife)

according to this you need iPhone 6 for cellular watch 3. a 5s needs latest IOS for GPS watch.

Set up your Apple Watch - Apple Support