Preheat oven to 400ºF with rack in the center.
Heat canola oil in a large, nonstick skillet over high heat. Add pork and brown for 2-3 minutes, breaking it up into small pieces with a wooden spoon. Add the celery and mushrooms, stir-fry for 1 minute, then add the cabbage, bean sprouts, water chestnuts, garlic and ginger, and cook 2-3 minutes more.
Stir in the tamari, then transfer the egg roll filling to a bowl and let cool. once cool enough to handle, mix in the egg to help the filling keep its shape in the baked rolls.
Roll out one sheet of phyllo dough on a large work surface. Paint the entire sheet with a little melted butter, paying extra attention to the outside edges. Place another whole sheet of phyllo on top of the buttered sheet, paint them with a little more butter and fold them both in half lengthwise.
Pile 1/8 of your mixture on the dough, two inches from the bottom of each side. Tuck bottom up and fold bot sides in, then roll and wrap upwards until you reach the edge of the dough sheet. Paint the seam at the end of the roll with butter and set it seam side down on a baking sheet. Repeat the process to make 8 rolls. (Phyllo dough dries out very quickly so as you are assembling the egg rolls, keep the remaining sheets covered with a damp kitchen towel.).
Transfer baking sheet to the oven and bake for 15 minutes, until lightly golden all over. Serve with dipping sauces and a simple salad with mandarin oranges alongside.