Because spoken words are not actually made up of neatly segmented and blended phonemes, a bit of cognitive blending gymnastics takes place within phonics instruction, to make the letters and sounds 'fit'. 

Phonics programmes manufacture this for a purpose, but it's important to recognise how often the two do not align easily. The more words are mapped, and the more children begin to understand the mapping phonemes and graphemes, the easier it becomes to read and spell words. In most cases, when you simply 'Show the Code', children will understand the Speech Sound Connection without explicit instruction.