There is no nation-wide ban on phosphated laundry detergents. Any bans are done on a local - city, county, state - basis. Basically areas around large bodies of still water, like the Great Lakes, New England, the Southeast, etc, have these bans. The arid Southwestern states, like California and Nevada, have no statewide bans (there may be restrictions in areas like Lake Tahoe, though). Out here, the main water pollutant of concern is nitrogen, not phosphorus.
Agricultural runoff is not the only source of phosphates. Humans excrete more phosphates on a daily basis than their washers would if, say, the detergents contained 8% phosphorus (about 30% STPP to detergent). Secondary and tertiary sewage treatment removes much of the phosphorus. Phosphates however tend not to be in run-off because they bind tightly with soil minerals and stay put. It's direct dumping of inadequately treated municipal sewage into ponds and lakes that can cause algal growth (but only when there is sufficient nitrogen already in the water). Muddy, turbid runoff of course might contain soil-bound phosphates.
TSP is typically not added to laundry detergents because it's not much better than cheaper washing soda. STPP is the form that is most effective, because it doesn't form a cement like precipitate on fabrics and on washer parts.
Until recently my favorite Mexican laundry detergent was Ariel. But I've noticed that in the past year, STPP has disappeared from the ingredient listing. So maybe P&G decided to pull it from the Mexican product sold in the USA, so it could be sold nation-wide instead of just in the Southwest.