Just tried it here, works as expected. Little bit slower when copying something on my iPhone and pasting it to my Mac, but it works. Maybe a stupid suggestion, but I think there might be a connection issue. I often find my iPhone struggling to find my Mac when for example using AirDrop, and then the other time it's the opposite (not being able to AirDrop to my iPhone). Could definitely be wrong of course, but at least you'll know Universal Clipboard DOES work in both ways with macOS Sierra beta 5 and iOS 10 beta 5.