I know we all agree that Phillip is an idiot but there is one thing he is right about: Letting personal feelings aside for the good of the territory, even though it is just an excuse in this situation.
Being close to the Sorcerer Kingdom a new country could be a pretty good source of new income for a small territory in the outskirt of a failing kingdom.
With the hindsight we have, of course it would be.
But under the impression the father has, that war will not break out soon and the kingdom still has a chance, he's not wrong in saying that a simple traitor from a small insignificant territory that probably won't be taken into account by the people who promised him the moon would more likely be crushed by either the sorcerer kingdom not upholding their word, or the neighbors he sold not trading with him for necessities he needs.
And importantly, as the father said, under different circumstances he would have nothing to offer. Literally they could just conquer his territory and do anything he offers themselves, under the pretense of liberating the people. He has no bargaining chips and
is only getting some attention as a trap for bigger things