Start by preparing the syrup. Combine the water, sugar, orange juice, the cinnamon stick and the orange blossom water, if you are using it. Bring the ingredients to a boil; once it starts boiling, reduce heat, and simmer uncovered for 15 minutes. Remove from heat and let cool completely.
While the syrup is being prepared, you must dry out the phyllo. We have found that the best, and easiest way to do this is to bake it. Preheat your oven to 200 degrees Fahrenheit. Open up your phyllo sheets, and one by one, scrunch them up, starting from the short side. After scrunching a sheet, place it on a baking pan and continue until you have used the entire pack of phyllo. You will need 2 baking sheets to accommodate all of your phyllo. Bake in the middle rack of your oven for 10 minutes. After the 10 minutes have passed, flip each phyllo sheet over and bake for an additional 8 minutes. Remove from the oven, and let sit for at least another 20 minutes, to further dry out the phyllo. With your hands, start tearing the phyllo into small pieces, and set them aside.
Note: We usually buy fresh phyllo sheets; however, if frozen is all you can find, go for it. Simply defrost your phyllo in the fridge overnight. Be sure to defrost the phyllo in the refrigerator as doing so on the counter will result in soggy phyllo sheets.
Preheat oven to 350 degrees.
In the large mixing bowl of a stand mixer combine the eggs and the sugar and beat for 3 - 4 minutes, until it is a pale yellow colour. Alternatively you can use a hand mixer.
Add the orange zest, Greek yoghurt, vanilla extract, baking powder, baking soda and salt, and mix until just combined.
Next add the oil and the orange juice to the bowl, and mix to combine well with the rest of the ingredients.
Using a rubber spatula begin to incorporate your dried out and torn phyllo into the cake batter, a little bit at a time. If you put all the pieces in at once, they will clump together.
After you have incorporated all of your phyllo into the batter, pour the mixture into a greased baking pan (we use a glass 9 X 13 baking pan). Bake for 50-60 minutes in the middle rack of your oven until your portokalopita is a nice golden colour.
Once your portokalopita is baked remove it from the oven and immediately pierce it in several places with a long clean skewer.
Pour your cooled syrup onto the hot cake, one ladle at at time. Allow each ladle to be absorbed into the cake before adding the next one. Repeat until all of the syrup has been used.
Let your cake cool for 2-3 hours before cutting, to allow the syrup to be fully absorbed.