Honestly, Phil already knew that Dilan and Kelan both had a superior intelligence, because the Warrior Spirits and the demons were full of praises for them, but so were Nolan and Alan... To Phil the twins were really like two peas in a pod, they both seemed carefree and liked to tease their loved one, but beyond that he also knew that they were really reliable during a big battle.
Only he never thought that they could be geniuses too.
Dilan then looked at him and he said, "It depends on what you call a genius... Kelan and I have an analytical ability that is a bit out of the ordinary, and Kelan also has a visual memory that allows him to remember exactly which book he saw which information in.
That's why he's so useful to the Warrior Spirits, not only is he quick when reading documents, but he remembers every detail and his analytical mind is at least as good as theirs.