Phase 1 is all about listening to sounds and learning to discriminate between different sounds. This is about sounds in everyday life, not just about sounds in words. Phase 1 lays the essential foundations for all the teaching that follows. If children can't hear sounds and differentiate between them then they will struggle to understand that words are 'built up' of sounds and that each sound is represented by a different letter or group of letters.
Letters are not introduced until Phase 2. If you have a nursery child or a child early in Reception then you will find these activities particularly useful. If your child is a little older but struggles to hear the 'separate sounds in words' then you might find it useful to return to some of these activities.