Learning phonics is learning by rote and then applying. Most brains see and remember patterns whether learning through phonics, by sight or a mixture of both. The children who get into trouble are those that struggle to see the patterns and recall the rote learning. Learning sight words has the advantage that you are learning something which can be supported by prior knowledge and context, learning by phonics has the advantage that if learnt efficiently the patterns are explicit, but it is still baffling for some children who struggle with remembering all the different phonemes that can be symbolised by a letter or common letter group, or who find it difficult to distinguish certain graphemes (b/d very common). The step from single sounds to blending is also a sticking point - children sometimes don't make that leap of understanding easily.