Orthography is the set of rules that dictates how to write correctly in a given language. In some languages, such as Spanish, those rules are essentially the same as the phonetic rules. English probably has the most inconsistent writing system in the world. This obviously creates a major barrier for your child. Studies show that dyslexia exists in all countries and all languages, but children with dyslexia in countries with phonetically regular languages have far less difficulty learning to read.
Studies show that good readers also rely more on their orthographic knowledge as they grow older. In fact, older children and adults often do not score as well as younger children on tests of phonemic awareness, as their knowledge of orthography supplants their phonological assumptions. For example, one researcher commonly uses a nonword, Jete, in testing phonological knowledge of rhyming patterns, assuming it will be correctly read as jēt. Experienced readers, however, might recognize the letter sequence as being a word imported from the French, pronounced as zhété.
Good English spellers rely heavily on their knowledge of morphology and visual memory of words. They will recognize a misspelled word on sight simply because it doesn't look right.
Your child's reading and spelling, as well as reading fluency, will improve tremendously as his orthographic knowledge improves; but unfortunately, this is another area where dyslexia stands in the way. Even if your child tries to visualize what the word ought to look like, he probably does not have a stable memory — after all, he may habitually reverse or transpose letters, and his memory of the correct spelling will tend to be obscured by his memory of all the times he spelled the word wrong. Your child will need special help to learn to correctly remember the visual appearance and letter sequence of words.