When he attains that level of mastery, his brain is freed up enough to focus on comprehension. He does it by practicing his newly acquired sounds until they become very, very familiar to him. During this time, he must not be distracted and frustrated with text which contains sounds he has not learned yet.
Decodable text is essential for beginning readers.
Laura Bush makes no mention of decodable text in her guide for parents. This is a weakness in her recommendations but could be easily added.