I have a 6 plus iPhone. Can this be paired with an Apple Watch?

If it is an actual iPhone 6 Plus not a 6S plus (note the s) .The Apple Watch in question would need to be running watchOS 5 or earlier. So any Apple Watch Series 4 or earlier with a compatible watchOS version can be paired to an iPhone 6.

If it is an iPhone 6s Plus, it can be any Apple Watch Series 7 or earlier running watchOS 8 or earlier.

What series watch? What watch iOS is currently on it? Apple Watch Ultra, Apple Watch Series 8, and Apple Watch SE require an iPhone 8 or later with iOS 16 or later.