Compatible? IPhone 11 and series 3 iWatch.

Yes.

See footnotes here: https://www.apple.com/apple-watch-series-3/

Apple Watch Series 3 requires an iPhone 6s or later with iOS 14 or later.

See here: https://macreports.com/apple-watch-not-getting-notifications-from-iphone-fix/

Restart both devices and check again.

If still not working, try unpairing and repairing the Apple Watch to the iPhone.

Make sure Do not disturb is not turned on.

my phone function on my iPhone watch is not working I don't receive calls what do I do?

it was previously working.