The phrase "don't fully agree" is correct and usable in written English.
You can use it when expressing partial disagreement with someone's opinion or statement.
Example: "While I appreciate your perspective, I don't fully agree with your conclusion."
Alternatives: "partially disagree" or "have some reservations".
"I don't fully agree [with Spacey]," he added.
"People feel they're shut out of the process if they don't fully agree with him".
Here is a rare point where I don't fully agree with Bradford.
Gardner has a quote in "On Becoming A Novelist" that I love, even if I don't fully agree with it: the purpose of art, he says, is to show people the proper beliefs and impulses.
We admit that the domestic trade in ivory should be banned in those situations where it can facilitate illegal trade but don't fully agree with the inclusion of the African elephant in 'Annex I' in those four countries.
After all, the T.S.A. screens two million people a day, many of them chronically irritated by rules with which they don't fully agree and by enforcement they sometimes consider arbitrary.
Moreover, members of Turkey's business and military elite do not fully agree with Mr. Erdogan.
Even the World Bank's leaders do not fully agree with Mr. Bush.
Economists do not fully agree about the macroeconomic effects of deficit spending, compared with the balanced-budget alternative, but they do agree that not all deficit spending is the same.
Boycotting Israeli universities, they note, actually hurts some of the occupation's most trenchant critics (and may thus be unlikely to bother Israeli hawks).Even fans of BDS do not fully agree on the best way forward.
Even if those countries suspect that Washington is trying to buy their support for a plan with which they do not fully agree, officials cite the compelling need to help underdeveloped parts of their countries susceptible to drug traffickers and guerrillas and to provide sources of income other than the narcotics trade for poor peasants.
