Preheat an oven to 375°F. Grease a round 11-inch pan.
Make the simple syrup, combine the water, sugar and lemon slices in a small saucepan over medium-high heat. Bring mixture to a boil, then reduce heat to simmer, stirring occasionally until the sugar is dissolved and the mixture is thickened but still clear colored, about 5-7 minutes. Remove from heat, add the rose water, and set aside to cool.
Use a food processor to chop the shredded phyllo dough into smaller pieces. Transfer the phyllo dough into a large mixing bowl. Pour the butter into the bowl. Use your hands to mix the butter with the dough, rubbing handfuls of the dough between your palms.
In another large bowl, mix together the ricotta, mozzarella and sugar.
Evenly spread the buttered phyllo dough into the prepared pan and firmly press it into the bottom and edges. Spread the cheese mixture onto the dough, leaving the edges around the pan empty.
Bake in the preheated oven until the cheese is slightly golden and the edges of dough are brown and bubbly, 20 to 25 minutes.
Remove the Knafeh from the oven. Place a large platter or baking sheet over the baking dish. Using oven mitts, carefully invert the baking dish onto the platter so the phyllo is on top. Pour the syrup over the Knafeh. Cut into pieces and serve while hot.