Preheat the oven to 400 degrees .
Add the oil to a preheated skillet set over medium to medium-high heat and cook the red bell pepper, celery, water chestnuts and onion for 2 to 3 minutes to soften. The veggies should still have a little crunch. Transfer to a bowl. Add the bean sprouts, crabmeat, soy sauce and thyme and combine well.
Paint half of 1 sheet of phyllo dough with the melted butter. Using the butter as glue, fold the sheet in half to form a rectangle. Pile about 1/3 cup of filling at the bottom of a narrow side, leaving a 2-inch border on 3 sides. To form the log, fold the bottom flap up and over the filling, fold in the sides and roll up to seal. (These are big spring rolls!) Paint the roll with melted butter and place, seam side down, onto a baking sheet. Repeat with the remaining sheets of phyllo dough. Bake in the center of the oven for 15 to 20 minutes, until lightly golden all over.