Hello,
Thank you for your question.
In our opinion, open phase would imply that there is no closure to the ideas. This implies that we have lots of ideas to resolve our customers' problems, however, we have not done anything about those ideas.
The ideas or solutions where we haven't really done anything about is not of any use to anyone. If we could assign a money value, the worth of those ideas would be zero.
So, divergent, in our opinion, implies that we are opening up till the point where we converge again (Check out the recent recording of the live session on Oct 9, 2020, where I have explained this in detail) in the Test phase.
This was our rationale in the options.
Hope this helps you
Thanks and have a nice day!