Put the flour and baking soda in the yoghurt and stir well. Beat the eggs in a bowl and add the crumbled feta cheese and yoghurt. Stir again.
Melt the butter and grease the tray. Put 1 phyllo pastry sheet in it and grease the top. Place a 2nd sheet on top, smear with butter again and sprinkle with the prepared filling.
Repeat in this order until you've run out of products. Bake in a preheated 392°F (200 °C) oven about 30 min. Take the hot phyllo pastry out and smear it with more butter.