The phrase "a key portion" is correct and usable in written English.
It can be used to emphasize the importance of a specific part of something, such as a document, argument, or process.
Example: "In our analysis, a key portion of the data indicates a significant trend that cannot be overlooked."
Alternatives: "an essential part" or "a crucial segment".
But in this book, Kurt Eichenwald has recorded a key portion of that story.
And maths plays its part in a key portion of News UK's editorial policy document to ensure "a safe, professional and effective working environment".
He offers a "reimagining" of a key portion of Baker's life, using half-truths and real elements to build a fractured picture of the celebrated jazz musician.
76ERS 83, NETS 79 Andre Iguodala scored 14 points, including 7 in a key portion of the third quarter, for visiting Philadelphia.
Notably, Barnett proposes an amendment that would effectively ratify the Supreme Court's decision in the Citizens United case, which struck down a key portion of the McCain-Feingold campaign-finance law.
A key portion of Interstate 80, where traffic has been slowed for more than two months since a tractor-trailer accident, is expected to be completely repaired by Monday morning, officials said.
For example, could proteolysis be eliminating a key regulatory portion of the protein?
The criteria included the understanding of the item question, the correct location in the key portion of the original passage, a full understanding of the located sentence(s), understanding of the options, and correct choice of the answer.
In another key portion of the session Denham confirmed that inferred data is personal data under the law.(Although of course Facebook has a different legal interpretation of this point).
"Consent should not be regarded as freely given if the data subject has no genuine or free choice or is unable to refuse or withdraw consent without detriment," runs one key portion of GDPR.
The key portion of training involved learning hit and run tactics of guerrilla warfare.
