Phosphates are expensive, not only in production but also in cleanup. They need to be removed from the wastewater, or they will disrupt the phosphor cycle and cause eutrophication. Admittedly, the phosphates contained in laundry detergent are unlikely to cause a major issue, being dwarfed by phosphate mining and water purification.

I believe the environmental concern is the reason recent editions of Tide have elected against phosphate use, and phosphate laundry powders need to be hunted down in retail stores (once, they were ubiquitous).