Is it possible to connect an iPhone to a WiFi network that you've previously connected your Mac to without having to enter the password on the phone?
As far as iCloud keychain goes, it will save a lot of your passwords that you enter on websites (as well as usernames) but I don't believe it will do it for wifi passwords.

Once you enter the password once on your iPhone though, it should remember it from then on, so you will not have to enter it each time.