No, they are not the same and they are not usually interchangeable. Phyllo dough (also spelled fillo or filo) comes from the Greek word meaning "leaf." They are paper-thin sheets of dough made mostly of flour and water, and are typically layered or wrapped around fillings to create layers of crispy, flaky dough when baked. Puff pastry is made by laminating dough and butter together. This entails wrapping a giant square of cold butter with dough and then folding, rolling, and chilling repetitively to create alternating butter and dough layers. When baked it puffs up to produce separate flaky layers and a crunchy exterior.