Letters by themselves mean nothing. It's when they're arranged in a certain order that they take on meaning. We advise teaching the sounds of the letters by making up short, common, words that the child already knows. However, at 2, the child may not be able to speak all these words clearly, since the vocal cords get hooked up when they get hooked up and the child learns to manipulate them properly. It's too bad that they can't use it in school, but it doesn't lend itself to large-class use, where each child's known words are different.
Consonants are easy to teach.
But don't hurry. This is a long-term project. Stick with one rule until the child learns it perfectly, and then go on to the next one. It's not their fault that those stupid guys who made up the written words used a different rule. That's correct, the word could be pronounced that way.