Two tried and true methods for keeping healthy, spotless planted tanks are Aqua Design Amano (ADA) and Estimative Index (EI). As I understand it, ADA uses rich substrates to provide most PO4 (and other things) to the plants and out of the reach of algae. PO4 in the water column is usually kept .6 ppm or below. EI, as I understand it, doesn't rely so heavily on substrates and keeps PO4 in the water column between 5-7 ppm.
Personally, I've found EI works for tanks that have all surfaces covered by plants, but grows algae on exposed hardscape. ADA seems to limit algae even with exposed hardscape.
If you're running a low tech tank, there are a couple more methods I've read good things about. These are the Walstad method and Sundeep's method. With these methods, PO4 levels are not specified as far as I can remember, but they probably are pretty low. (Sudeep does give dosing guidelines.) There's lot's of info out there for the Walstad method. But, if you're curious, this is Sundeep's article: