Phonics based reading is teaching children to read using Letter Sounds and Letter Symbols.
Letter Sounds are the sounds that Letters make. Letter Symbols are the Letter of the Alphabet.
Phonics lessons teach children to break apart words into their sounds in order to read and decode unfamiliar words in text.
If your child is reading without being able to sound out words, I would still recommend that you teach your child Phonics.
Phonics and Letter Sounds are also a really good way to help your child learn the Spelling of words.
I also think knowing Phonics and how to blend sounds would only equip your child with additional reading tools that he/she could use when he/she come across unfamiliar words in text.