My response is coming from doing my degrees in socio-psycho linguistics. My focus was on social and psychological pragmatics and psychological interaction with social systems, so I don’t have all the phonics and phonology oriented information other commenters have already shared. Just a caveat.

I just wanted to say that 4 is still developmentally pretty young, and kids that young are observant sponges. In addition to the more reading-based education people have shared, a good supplement is still for you to read to your LO and pointing to the words as you read them. The more diversified and casually a child is exposed to an idea, the more likely they are to learn, retain, and apply it themselves.