There are two different chemicals. There is Phosphoric acid, which can be used in sodas, mostly Colas. Open Cola has an amount of phosphoric acid added to it for example. There is also Acid phosphate, which is created from a reaction of phosphoric acid and a calcium, magnesium or potassium salt to reduce the acidity. What you get is just pure sourness. The lime phosphate was most likely created using acid phosphate.
Artofdrink, linked in the acid phosphate link, sells acid phosphate, and also has a few soda recipes such as a chocolate phosphate and cherry phosphate. I was drawn to the website from an article in imbibe magazine last year.
For a lime phosphate... I'd probably wind up using citric acid for the sourness.
Secondary: GF Czech Lager
Waiting to be kegged, Italian Primitivo
Kegged&Ready: GF Orange&Coriander, GF Honey Lager, GF chocolate ale, GF English ale, Island mist (zinfandel), Island mist (cbry malbec).
Bottled: Infected Mead, Dry Hard ciders, Accidental Sorghumwine, various unnamed.