A blend of shrink and inflation, the noun shrinkflation denotes the practice of reducing a product’s amount or volume per unit while continuing to offer it at the same price.

This noun occurs, for example, in Shrinkflation: don’t want to upset customers with price rises? Just make your product smaller, by Jonathan Barrett, published in The Guardian (London and Manchester, England) of Friday 16^th June 2023:

While shoppers fixate on the rising cost of their weekly food bill, another far more clandestine price increase is sneaking into their shopping trolley.
Known as “shrinkflation”, food companies are regularly reducing the size of their products but not the price, burdening consumers already grappling with surging household costs.
A growing list of companies are doing so to pass on costs and increase profits by avoiding a sensitive price hike that is more likely to attract the ire of customers.

It was apparently the U.S. economist Philippa ‘Pippa’ Malmgren (born 1962) who coined shrinkflation as currently used. The texts containing the earliest occurrences of this noun that I have found indeed refer to her—these texts are as follows, in chronological order:

1-: From From Chocolate to Beer, Shrinkflation Is Unseen Pressure, by Simon Kennedy, published in Bloomberg on Wednesday 3^rd September 2014:

Inflation may be lurking in the aisles of supermarkets.
Even with price pressures tame to non-existent in the industrial world, economist Pippa Malmgren says they’re there if you look.
A former adviser to President George W. Bush, Malmgren is zeroing in on what’s come to be known as “shrinkflation,” where companies charge consumers the same—or more—for less. That may foreshadow an overall jump in prices, an alarm she’s been sounding for a while.
“Shrinking the size of goods is exactly what happened in the 1970s just before inflation proper set in,” she writes in her new book, “Signals: The Breakdown of the Social Contract and the Rise of Geopolitics.” ¹

¹ Signals: The Breakdown of the Social Contract and the Rise of Geopolitics was first published by Grosvenor House Publishing Limited in 2015.

2-: From Shrinkflation: Coke, Pepsi Shrinking Soda Cans and Cost More, by Andrew Moran, published in PFhub™ on Wednesday 14^th January 2015:

In the last couple of years, consumers have been noticing that the products they purchase are getting smaller but they still cost the same, or even more. This isn’t a conspiracy. Items are shrinking in size and come with a price-tag that’s the same or higher. It is known as shrinkflation, which is essentially a prelude to price inflation.
This past summer, Pippa Malmgren, economist and advisor to former President George W. Bush, told Bloomberg News that the trend in the marketplace has been for companies to charge more for less. According to Malmgren, this would be the very first step towards rapid spikes in prices.

3-: From the London Evening Standard (London, England) of Tuesday 21^st June 2016:

Why we’re all suffering from electile dysfunction

THE world economy is facing unprecedented difficulties. Never in history have so many governments done so much to restore their economies with such limited results. New realities need new words, so here is the new economic lexicon.
[…]
Electile dysfunction
The inability to become aroused by any political candidates or their policies.
[…]
Shrinkflation
The process by which the consumer pays the same price as ever for a product but now finds far less of the product inside the packaging. Cereal boxes are now only half full and crisp packets contain far fewer crisps.
[…]
Dr Pippa Malmgren is the author of SIGNALS: How Everyday Signs Can Help us Navigate the World’s Turbulent Economy ², published by Weidenfeld & Nicolson, price £20

² This book was first published in 2016.

4-: From an article by Jamey Keaten, of Associated Press, published in several newspapers on Wednesday 9^th November 2016—for example in the Times Leader (Wilkes-Barre, Pennsylvania, USA):

GENEVA—More valleys, fewer peaks: The maker of Toblerone Swiss chocolate has widened the spaces in some of its iconic, triangle-array bars, offering about 10 percent less product for the same price. Fans are outraged.
[…]
Economist Pippa Malmgren, who has studied what she calls the corporate practice of “shrinkflation,” believes the company was using the recent political situation in Britain to test to see if people would notice.
“Whole divisions of major companies” are devoted to shrinking a product while keeping the price stable, she noted. She estimated that about 10 percent of the Toblerone candy bar was dropped.
“This is an art form,” she said. “This is not random.”

I have, however, found earlier occurrences of the noun shrinkflation, but not used in the current sense, in the following two texts:

1-: Investing: To Buy Or Not To Buy?, by Steven C. Swett, Valley News staff writer, published in the Valley News (West Lebanon, New Hampshire, USA) of Tuesday 8^th January 1991—Ellis L. Phillips Jr. was then head of the Ellis L. Phillips Foundation, which makes grants of an entrepreneurial nature:

Phillips points to major weaknesses in the U.S. monetary system, which he believes is flawed; to substantial debt now being carried by government, corporations and individuals, which he sees as too high; and to a condition he calls “shrinkflation,” which is depressing the value of assets.
He sees a condition developing where substantial numbers of people might simply walk away from their assets—be it a car or home, because they cannot afford to keep up the payments. “That is when the bubble bursts—when people can’t afford to pay higher costs.”

2-: Econoclasts: The Rebels Who Sparked the Supply-Side Revolution and Restored American Prosperity (Wilmington, Delaware: ISI Books, 2009), by Brian Domitrovic:

Following World War II, the United States traded depression for an acute period of stagflation. Actually, it was “shrinkflation,” in that the economy was contracting as prices surged.
The 34 percent depreciation of the dollar by 1948 was sufficient to erase any excess gold that the United States had been hoarding since the 1930s, when it was sterilizing the gold coming in from trade with European belligerents. During the war, the United States started unsterilizing the gold—that is, printing money in the absence of gains in the real economy. After 1948, if inflation was to occur at all in the American economy, markets would push gold above $35 and jeopardize Bretton Woods.
Shrinkflation was a puzzling experience. It confounded the president, Harry Truman. And yet shrinkflation did play into the government’s hands in one way. It enabled the national debt to be cut down.