Your kid now can understand the relationship between sounds and letters. They will not mistake commonly used words and phrases. You can also observe that they can break words into syllables and thus can read and spell unknown words. They will categorize words into similarly sounding words and also can spot mistakes in what they have written.
What you need to do
Teach your child the technique to read aloud, write, remember and check on what they have learnt. This helps them to correct their spellings. Introduce them to use of a dictionary to learn the meaning of new words and also to correct spelling mistakes.
If your kid is eager and interested to spell new and difficult words, let them play with word building games and also enroll them in spelling bee contests. They will now have the knowledge to know that bigger words are made of smaller words, and are conversely finding that smaller words can be made out of a bigger word. Practising these techniques would be a great pastime for them to learn newer words, understand their meaning and also to learn spellings.