Preheat oven to 425 degrees. In a small bowl, combine spinach, cream cheese, and garlic and season with salt and pepper.
Lay 1 sheet phyllo on a work surface and lightly brush with butter. (Keep extra phyllo covered while you work.) Stack 2 more sheets on top, brushing each with butter. Cut stack in half crosswise. Repeat with remaining 3 sheets phyllo and more butter to make 4 stacks total.
Season salmon with salt and pepper, then place 1 fillet in center of each stack and top with spinach mixture. Fold 2 opposite sides of each stack over spinach mixture and tuck other 2 sides beneath to form a packet. Brush tops and sides with butter. Bake packets on a parchment-lined baking sheet until golden brown, about 10 minutes.