The following is anecdote, the plural of which is not data! However, i am the parent of a child who taught himself to read by 'reverse engineering' - ie working out the phonic code for himself. I would have thought that he was reading by word recognition, but his Reception teacher established that actually he had an extensive and accurate knowledge of phonics.
In his case, he would recite books as mrz describes - absolutely accurate word for word recall, including turning pages at exactly the same point as the 'real reader' did, and following along with his finger under the words as the person reading the book to him did.
From that, he matched words in print to the spoken sound of words - but what it turned out he was also dong was linking phonemes to graphemes - ie the constituent parts of word to their constituent sounds. He could then apply that phonic knowledge to read new words, and also to encode words.
So it is not that self-taught readers don't use phonics, IME. It is that they use known words to work out the phonic code before it is explicitly taught to them. It is obviously more efficient to teach the phonic code directly, rather than to rely on children working it out for themselves, but pre-school readers who are determined to read don't necessarily wait for that explicit teaching!
DD learned to read at school, using phonics. By about the start of Y1, she was as good a reader as DS had been at the same age, despite his earlier start. DS has remained a better speller, possibly because of the early use of visual memory in his learning strategy, so he remembers the 'look' of the correct alternative phoneme / grapheme correspondence more readily.