The simple answer to your question is that homeopathic remedies don't do anything. At best, they rely on the plecebo effect. Many of the remedies are basically just water with perhaps some other things in it that are known not to have any effect on people.
Allergies are caused by your immune system being activated by everyday harmless things. Basically, one of life's biggest enemies is the virus. Bacteria, yeast, flies, bears, humans are all attacked and killed by viruses. Keep in mind that it was a virus that killed as many people as WWI during that time frame - they are very dangerous to us. We have evolved a complicated defence system called the immune response (we also have a few other defence systems too).
The viruses themselves are DNA (the stuff that makes up our genome) or RNA (very similar to DNA) or both. However, DNA and RNA don't survive very well outside host cells (and most of life produce RNases which destroy RNA to kill viruses and make scientist lives more difficult). So they package themselves in "coats" that protect them in the outside world. Since these "coats" are made on what amount to miniture assembly lines, they are basically identical. So part of the genius of the immune system is to produce proteins called antibodies that specifically recognize the shape of the coat for a given virus and cause the virus to be degraded.
Unfortunately, the viruses can evolve so that there coats shapes are different. To counter this, our immune system uses a system of antibody production that allows it to recognize a near infinite number of shapes. When it recognizes a shape associated with a virus, it causes more of that particular antibody to be produced so that the person is immune to that virus. Unfortunately, sometimes the shape is not associated with a virus, but rather some normal thing like peanut butter. And when the immune defence is triggered, it can create a severe reaction (its kind of like the US allowing torture in order to prevent a terrorist attack).
So what is water or calcium phosphate going to do to prevent antibodies from recognizing an antigen (which would be the virus for an antibody doing its job or peanut butter for somebody with an allergy)? Obviously nothing. And if it was doing something, think how dangerous that could be. Viruses don't kill many people these days, but they do in people that have weakened immune systems.
But I wouldn't be worried. Homeopathic remedies don't do anything.