en.wikipedia.org/wiki/Phosphoric_acid#Food_additivePhosphoric acid is used for the main soft drinks like Coca Cola. Fifty percent of Crohn's patients have lower-than-normal bone density. Kidney stones and crystals are also more common in Crohn's patients.
"The study does not examine the effect of phosphoric acid, which binds with magnesium and calcium in the digestive tract to form salts that are not absorbed, but rather studies general phosphorus intake."
If these salts are not being absorbed, they are quickly passing through your intestines. Many of us do not wish to speed up our bowel movements. Also, if it is attaching to calcium, that will reduce the amount of calcium available in the body for your bones. In an ordinary person, the loss may be negligible, but for us, it is a risk.
If you have trouble reducing your soda consumption, I recommend caffeine-free soda and then low-sugar sodas. I myself have trouble weaning from soda.