Yeah, if you put the bones in concentrated phosphoric acid and wait days and days for the bones to dissolve. . . but by the time a diet drink goes into your STOMACH which has an acidic level far higher than any diet or sugared soda, it really doesn't mean much of anything that study found. That was totally bogus.
Your stomach acid, usually strong hydrochloric acid can be as low as Ph of 1. The phosphoric acid in a soda averages Ph of 2.5. The lower the Ph, the more acidic the fluid is. Ergo, your stomach fluid is far more acidic than is your soda.
By the time any phosphoric acid gets from your bowels and into your blood stream, it is just a source of phosphorus. . . a bone building block. Soda cannot dissolve living bone.