The phrase "an untold amount" is correct and usable in written English.
It can be used to describe a quantity that is so large or indefinite that it cannot be easily measured or expressed.
Example: "The charity received an untold amount of donations after the disaster, allowing them to provide aid to countless families in need."
Alternatives: "an immeasurable amount" or "a vast amount".
"If you're good at it, there's an untold amount of work," he said.
He grabbed 15 rebounds, blocked 3 shots and altered an untold amount of attempts in the paint.
Even the smoothest birth is testing and most women go through an untold amount of challenges to their self-esteem, beliefs and ego.
The gesture cost him an untold amount of money but consolidated his reputation as a man of principle, especially among younger war protesters.
He spent ninety-five thousand dollars a month on jewelry and clothing, $411,777 on pigeons and cats, and an untold amount on pet lions, tigers, and "royal blood" Shar-Peis.
Once an email platform for a company still managing an all-but-defunct computer language, Symbolics.com was bought for an untold amount of money and turned into a platform intended to serve ads to the unsuspecting visitor.
All this squandered sustenance is a sin where the environment is concerned as well, since it's estimated that food waste accounts for one-quarter of all freshwater consumption, more than 300 million barrels of oil a year, and untold amounts of pesticides and fertilizer.
On a personal note, I'm going to have to declare the fact that I see Phil Wilkinson around London events now and again (though not socially, I might add) and I think no-one would disagree with me in saying that he is a nice guy with untold amounts of enthusiasm and energy.
After F.D.A. approval, the manufacturer of Botox plans to spend untold amounts in a campaign to convince more women that they should shell out at least $1,000 each year on this elixir.
His pantsless jaunt through Kansas City made a pretty big splash, with untold amounts of incriminating evidence making it onto Snapchat, overhead traffic cams, and the local news.
These were the days when record companies were still getting their heads around digital, and one of the perks of a music journalist's working life was to receive untold amounts of clutter through the post; a deluge of CDs, band T-shirts, DVDs, occasional vinyl and weird, bespoke merchandise that only served to perplex.
