Hi ElizaJane
as I described my problem was that Outlook would not take anything in its Calendar from the iCloud whereas the opposite (from outlook vial iCloud to iPhone worked), so I'm not sure if you are having exactly the same problem.
I also am a bit surprised that my simple solution fixed it, as I have read through many forums and saw that other are having the same problem without solutions, and I simply can't imagine nobody has tried what I did, so it might just as well be a lucky thing for me.
having said that what i did was going to the WINDOWS SYSTEM CONTROL and to the option where you de-install software. upon finding the iCloud Software there, which i had installe somtime in March or so i clicked the CHANGE option and then was asked to either FIX it or DEINSTALL it. I chose FIX and what it did was a REINSTALL of the software, I assume with a newer version of iCloud.
I had to do the same things and settings as I had when I installed the iCloud for the first time back in March, but it was a quick thing to do. the only thing was that I had some calendar duplicates then, but I just left-clicked them to see if they were indeed duplicates or even empty ones and then right-clicked on them and deleted them.
Yeah, after that everything worked both ways again, indeed much faster than before, an entry made on my iPhone shows already after about 5 seconds now on Outlook
Hope this works for you too!
greets,