1) I'm talking about bacteria, not yeast.
2) Strains that can easily tolerate 20% aren't really abundantly floating around, or even over 10-15% for that matter.
3) Malta Goya is filtered.
4) You're wrong about the pH. Cola is more acidic than lemon juice. pH of lemon juice = ~3.28-2.5. pH of cola = ~ 1.75-2.75. pH of beer = ~ 4.
Science seems to disagree with you:
Analysis of preservatives in soft drink beverages: News from Metrohm UK
My man, I'm not trying to start a thing over phosphoric acid, because I could really care less, but my father is a VP at a bottling plant, and I've gone into the lab there to get food grade phosphoric acid on numerous occasions for various purposes, and have had this exact same conversation with the techs.
It provides a tangy or sour taste and, being a mass-produced chemical, is available cheaply and in large quantities. The low cost and bulk availability is unlike more expensive natural seasonings that give comparable flavors, such as citric acid which is obtainable from lemons and limes.
This is a write up on food grade phosphoric from Wiki. Not the best source, but it more or less validates what I'm trying to get across. Does it acidify the cola? To an extent, yes. But the acidic nature of the drink has to do with a cornucopia of ingredients plus an abundance of dissolved CO2 (carbonic acid).
Sodium benzoate is a real preservative, targeting microbial activity. This is what Wiki has to say about SB:
Sodium benzoate is a preservative. It is bacteriostatic and fungistatic under acidic conditions. It is used most prevalently in acidic foods such as salad dressings (vinegar), carbonated drinks (carbonic acid), jams and fruit juices (citric acid), pickles (vinegar), and condiments.
Again, the phosphoric acid is added for flavor; the effect it has on pH is a concern to bottlers only insofar as it impacts the other ingredients, it is not added as a preservative. They use sodium benzoate for that purpose.
Case in point: if SB was added to Goya Malta, diluting it 50/50 with water would not save it from being unfermentable and deadly to yeast. But the phosphoric acid is no biggie (ie: it's not the greatest of preservatives, and is not intended for that purpose).
Not trying to split hairs, but when someone is consistently telling me I'm wrong, I gotta defend myself.