You may see this label on detergents and soaps. The primary reason for using phosphate-free soaps/detergents is to reduce our impact on surrounding water. aquatic life and in particular fish.

 Phosphates travel through our drains into our water bodies (oceans, rivers, ponds,creeks etc). Ponds covered in algae, may be caused by excessive phosphate from our water ways. Just as agricultural fertilizers include phosphate to accelerate the growth of plants, phosphates do the same for aquatic plants. This is an issue when the decomposition of these aquatic plants (algae, seaweeds etc.) extracts excessive oxygen which fish and other organisms require. Algal blooms, dead zones, red, brown and gold tides are all ways excessive phosphates affect our coastlines and eventually our health.