Can an Apple Watch Series 3 be used if I am using version 16.3.1 on my phone?

Hi there Bmansmom,

Thank you for posting to Apple Support Communities.

An Apple Watch Series 3 requires an iPhone 6s or later with the latest iOS version. This is according to the Apple Watch Series 3 Tech Specs: Apple Watch Series 3 - Technical Specifications

Make sure your iPhone is updated to the latest version of iOS. Before updating, we recommend backing up your iPhone first. These articles can be of help. When you back up, you can back up using a Mac or PC rather than iCloud if you choose.

How to back up your iPhone, iPad, and iPod touch

Update iOS on iPhone

It's also a good article that you referenced with If you can't pair an Apple Watch with your iPhone - Apple Support

If you're still having trouble pairing your Apple Watch, contact Apple Support: Get Support

Take care.