Preheat oven to 375 degrees. Spray a large baking sheet with nonstick spray; set aside.
Heat olive oil in a large skillet (12-inch diameter or larger) over medium-high heat.
Add shallots to oil and season with salt and pepper. Cook until they start turning translucent, stirring frequently (a couple minutes).
Add mushrooms to shallots, mixing well. Cook until liquid released from mushrooms has totally evaporated and mushrooms are beginning to brown, about 20 minutes.
Remove mushrooms from heat and season generously with salt and pepper.
Stir cream cheese into mushrooms, mixing until completely incorporated; then, mix in sour cream, parsley, and green onion. Season mixture generously with salt and pepper to taste. Set aside.
Lay one sheet of phyllo dough on a flat surface. Cover unused dough with waxed paper (or plastic wrap), and then a damp towel. Brush dough lightly with butter, then top with another sheet of phyllo. Add two more layers of dough, brushing with butter in between the layers (always keeping unused phyllo covered). Then, top with one more sheet of dough. Do no brush this last layer with butter. (You should have 5 layers of dough.)
Cut rectangle of phyllo in half so you have two squares. Top one square with 1/8 of the mushroom filling, about one inch from one of the edges.
Turn the bottom edge of dough up over filling, then fold in sides. Roll up dough and filling (similar to how you would a burrito) and place seam side down on baking sheet.
Brush top of strudel with butter, then repeat process with remaining dough and filling. You should have 8 strudels.
Bake strudels for about 35 minutes or until golden brown all over.
Serve strudels hot. Enjoy!
If you prefer, you can also prepare 2 large strudels instead of 8 small strudels. Simply layer 10 sheets of phyllo using the process described above, then top with 1/2 of the mushroom mixture. Roll up as described, then repeat process with remaining dough and filling. It should take about the same time to bake as the smaller rolls.