Guided Play is important because each new skill builds on what the child has already learned.
Each phonological activity plays an crucial role in teaching a child to become a confident reader. If the child has not mastered a particular sound or skill, s/he will not be ready for next activities.
For example, in the Cave of Sounds a child is introduced to new sounds. It is important they learn and master this before moving onto other activities such as the Cake Factory. In the Cake Factory they will use the sounds they learned to decode and blend words.
Without Guided Play, a child may favour certain activities and miss skills needed to become a confident reader.