It’s a mistaken notion that all carbonated soft drinks are rich in the chemical element phosphorus (which almost everyone, it seems, wants to misspell as “phosphorous”). The only thing that all carbonated soft drinks have in common is carbonated water: carbon dioxide dissolved in water.
Beyond that, they contain a wide variety of flavorings and other ingredients.
A few of them, including Coca-Cola, Pepsi-Cola, and some other colas (sodas containing the caffeine-rich extract of tropical kola nuts) do contain phosphoric acid. It’s a weak acid of phosphorus, just as the carbonated water itself is a weak acid of carbon: carbonic acid.
All acids taste sour, and the phosphoric acid is there to increase the acidity and provide a bit more of a tang to set off the sweetness. Phosphoric acid is also used to acidify and flavor baked goods, candies, and processed cheeses.
About the bone-weakening effect: Maybe the study was limited to phosphorus-containing colas. Even so, just as one rose does not a summer make, neither does one study prove a cause-and-effect relationship between Cokes and bones.