In English, phonics for reading is different from using it for writing.
For reading, many children need very little phonics. They take only a short while to learn the sounds for consonants, such as b, d, g, and the main sounds for vowels (ca, co, cu, ke, ki, see, out, too), and move on to recognise more and more words by sight, without the need for decoding (as we all can now). In cases of uncertainty (foot, boot; speak, break), they use the other letters in the word, or context, or meaning of the sentence (read last night, read every day) to work out the right sounds.
For writing, all children have to learn to break words down into their sounds and to use the right letters for them. Remembering the right spellings for sounds which have several (late, eight, play, they) is also much trickier than learning to read such words, especially the ones which are completely unpredictable (see, me, tea, ski, key).
Phonics, in the sense of learning the regular sounds for spellings and converting sounds into regular spelling patterns, is of more limited use for learning to write English, because English spelling is very irregular.
Correct spelling depends more on imprinting the right look of words on our brains, which isn't really phonics at all. The passionate advocates of phonics have lately made matters more confusing by insisting that learning to read involves nothing but phonics, and calling all teaching of reading and writing phonics.
Masha Bell