NEW YORK — It’s Dec. 17 and a customer at the Old Navy on 18th Street and Sixth Avenue in Manhattan has a problem: She’s looking to get matching Jingle Jammies for her family but can’t find a size 3T for her son.

Daisy Tecotl has a solution. She checks the In Stock On Shelf app on her store-issued mobile device to see if there’s a 3T in the stockroom. There isn’t, so she opens the Order In Store app and arranges to ship it to the woman before Christmas.

The sale is reflected in yet another app, the Sell app, that pings Tecotl, a 24-year-old merchandising manager, with hourly figures on sales and credit card sign-ups and several other metrics, which she uses to broadcast guidance to “refocus” her sales associates, who, like her, are outfitted with earpieces and walkie-talkies.

This is the job of a retail clothing worker at the end of 2019: dashing back and forth between stockroom and fitting room and sales floor, online and in-store, juggling the hats of cashier and cheerleader and personal shopper and visual merchandiser and database manager.

As brick-and-mortar stores scramble to justify their continued existence, they’re trying to be all things to all customers, to blend instant gratification and infinite selection. And it falls upon the workers on the front lines to make it all happen.

Entry-level associates at Old Navy have store-issued mobile devices, too, that do things like ping them when a customer buys the last item in a particular size so they can replenish it from a stockroom that holds more than 250,000 items, or ring up customers anywhere in the store’s 30,000-square-foot, three-story expanse, or notify them of a BOPIS — that’s Buy Online Pickup In Store, which sends an associate to find the items on the sales floor.

In New York City, retail clothing jobs declined by 9% from 2013 to 2018, even as overall employment in the city jumped about 14%. A report last week by the Center for an Urban Future found that the number of national retail chain stores in the city shrank 4% this year, the biggest drop since at least 2008.

Old Navy hopes to buck the trend. It has performed so much better than its sister chains in the Gap empire that Gap Inc. decided in February to spin off Old Navy into its own company — one that plans to open 800 new stores, despite a dip in sales this year.

But to compete in a world where Amazon moves mountains of merchandise without a retail sales force takes a particular focus, said Saravanan Kesavan, associate professor of operations at the University of North Carolina’s Kenan-Flagler Business School.

“Retail for the most part is not a place where they’re looking for salespeople,” he said. “They’re looking for retail transaction enablers.”

At every shift, each Old Navy store employee on the sales floor is issued a “Ticket To Win,” which the company describes as “a contest-driven tool” to help managers and associates “focus on how best to serve the customer and drive business results.”