The phrase "principally interested" is correct and commonly used in written English.
It means to be primarily or mainly interested in something. Example: "The CEO was principally interested in increasing company profits rather than improving employee satisfaction."
we are principally, interested by the "Retain" step.
North Vietnam is principally interested in French machine ry.
He did a good deal of cycling growing up, but he was principally interested in golf.
It is designed to prove that Sherman did an incompetent job, but Bishop seems principally interested in proving that Skakel was in fact not guilty of the murder.
Although it will report unfolding operational developments rapidly up the chain of command, it is principally interested in moods and intentions.
And it won't be the Chinese who are principally interested in cutting their energy imports and exporting current generation clean energy, not developing technology to save the planet.
Thus it was that England relied instead on private trading companies, which were interested principally in commercial rather than territorial expansion, to defend its interests in the expanding European world.
The younger boy is 9, but somewhat older in intelligence, and very special in his tastes, since he is interested principally in things of a cultural nature.
The notion of humans as neither good nor bad but interested principally in survival and the maximization of their own pleasure led to radical political theories.
Many outsiders suspected that the Texan oilman in the White House was interested principally in the country's oil reserves, the second-biggest in the world.
The Middle Eastern Studies concentration is designed for students interested principally in the art and architecture, culture, economics, history, and politics of the Arab world, Iran, Israel, and Turkey.
