The actual amount of phosphorus in a coke zero is pretty small. First thing I’ll ask, how long have you fasted for? The main reason for phosphorus is it heavily reduces the odds or refeeding syndrome. The thing about refeeding syndrome though, is that it’s wildly overblown, and mainly an issue for someone who was malnourished.
For example, look at images of people from the holocaust, and realize only a small fraction of those people had it. If you’re a well nourished person, it’s likely not a big concern, and at worst you might feel crappy.
That said, if you want to make sure you intake phosphorus, there are other good options. Obviously a straight phosphorus supplement is good, but let’s compare other options. Your coke zero has around 55mg of it, 1 cup of chicken has 300mg, 3 Oz of pork has about 200mg, organ meats have an INSANE amount, fishes range from 200-400ish mg for a small portion, dairy products like milk and cheese hold similar amounts as the rest,sunflower seeds, nuts, and beans are also rich in it.
So if you’re worried about it, just make sure you either take a phosphorus supplement, or make your first meal high in phosphorus. Your coke zero isn’t hurting, but it’s not doing a whole lot on its own. Also, like I said, it’s more than likely a non issue if you are well nourished before your fast.