“we told set representation of FDD and ZDD are the same.”
Here, you need to be precise! FDD and ZDD have different semantics although they semantically fall into the same category. When you see a diagram that could be interpreted as a ZDD, it could also be interpreted as an FDD. But it would typically implement a different formula. The set representation is just a way to represent the diagram. This means that a set representation of diagram only tells you how the diagram looks like. It doesn't tell you whether the diagram is understood as an FDD or a ZDD.
You did correctly write down the set representation of the diagram you were presented.
However, that wasn't the (whole) task. The given diagram is supposed to be read as an FDD representation of the formula ϕ. You should create a ZDD representation of this formula ϕ. That ZDD you should submit in its set representation.
Spoiler-Warning: Here's how to do it.
Take the set representation of the FDD. (You already correctly computed that) Write the FDD as a RMNF-Formula. Convert the RMNF-formula to a ZDD. For example, you can fill a eight line truth table or just build the ZDD from the formula. Then you read the set representation from the ZDD, just like you already did it for the FDD.