Let's start with where the word 'Phonics' comes from: it is based upon the Greek word, 'phone' which simply means sound. In Phonics, a student is matching a sound with a letter (or group of letters), stringing them together and forming up words.
The English language has 44 distinct sounds and about 77 ways to represent them. Yes, it's about 77! I haven't counted them all but even a simple letter like 'a' can make the short sound as in 'cat' and a long sound as in 'cake' and even sound like a very short 'u' as in the word 'attempt'! For another example, I am sure you are familiar with the odd letter combinations our language utilizes to make the sound of the letter 'f.' The 'ph' combination is used - as in the word 'phantom' and even 'gh' makes an 'f' sound when used in the word 'enough' and don't forget, we can double the letters - for no apparent reason - and spell 'stuff.'
The reason that English is so complex in this regard is the same reason that it is one of the richest languages on earth: it is a conglomerate of many other languages. I guess there is a price to pay for everything!
The good news is, if you can master 77 different letters and combinations of letters, you can read literally millions of words. In stark contrast, when a sight reader has committed 77 different words to memory, that is all he has. Seventy seven words and no open pathway to reading any more or any less.
The question I would ask is this: do you want your child locked into the memorization mode or do you want him being able to decode his own written language and pursue the adventure of reading at his own pace and pleasure?