You can easily work on phoneme frames using a whiteboard. Children soon learn to divide the board up into 2, 3, 4 or 5 box phoneme frames. Read a list of words with 3 sounds. One by one the child must write each sound into a box on the phoneme frame. Some children need help to know where to start their word so I always put a red dot for the first sound.
Use the whiteboard as a 4 or 5 box phoneme frame or use words with 3 sounds but more letters. For example b/oa/t, l/igh/t, p/ai/n