ST. LOUIS — Joe Kelso and his wife, Teresa, were out for pizza in Chesterfield, Mo., earlier this year when they noticed a family of six sitting nearby in complete silence.

“It was very eerie,” said Joe Kelso, 31. “They all had iPhones out, and none of them was saying a word to each other.”

The Kelsos say the observation reaffirmed their aversion to smartphones at a time when a majority of Americans have turned to the devices over their stripped-down cellular siblings. The Valley Park couple prefer “dumbphones” — slang for cell phones that only make calls and send text messages — putting the Kelsos among an endangered species of smartphone holdouts.

Separate studies published this year by the Pew Research Center and Nielsen said more than half of Americans now own smartphones, up nearly 20 percent from last year. Many Americans will set out on Black Friday to buy the fancy devices and pricey accessories for themselves and loved ones, some using apps on their phones to find the best deals.

But loyalists to “feature phones” — as the industry prefers to call basic cell phones — say they resist the switch because they fear becoming addicted to the devices to the detriment of face-to-face human connections. Others shun smartphones because of higher costs or from an anti-consumerist pride in the face of an onslaught of marketing.

Margaret Kelly, 26, a cosmetologist-in-training from Maryland Heights who uses a flip phone that came free with her plan, said she’s a dumbphone user partly because of the expense. Between the more pricey phones and the higher cost of data plans, dumbphone users can save cash sticking with simpler devices.

She said she also worries a smartphone would usurp time spent with her 13-month-old son, Josiah.

“He’ll be like, ‘Hold me,’ when I’ve been doing something else for too long,” she said. “I don’t want the computer and phone to be all he knows.”

Others who hold on to their basic phones share Kelly’s concerns, despite being seen in some circles as Luddites.

Joe Ballard, 35, a highway construction worker from Belleville, Ill., brushes off his friends’ teasing about his flip phone. He says the phone he has is smart enough for him. Ballard prefers simpler, more durable phones that withstand the rain and dust he encounters on the job.

He also gets frustrated when out with friends who compulsively use their phones to check email and social media.

“I’ve been at a restaurant with friends, and me and my girl are trying to have a conversation while they’re all Facebooking, checking this out and checking that out,” he said. “You don’t need to do all that. You should just be out having a good time.”

One local dumbphone user, Darnell Lee, fears manufacturers will stop making basic phones.

Lee, 77, a retired mechanic from north St. Louis County, said he was tempted into a smartphone a few years ago, but quickly got rid of it and went back to a flip phone because he didn’t need all of the smartphone’s features. Lee’s flip phone, held together with Scotch tape, makes calls, sends texts and takes low-resolution pictures. He said that’s all he needs.

Demand for smartphones continues to grow apace, but manufacturers are likely to continue making basic phones as long as there is demand, said John Walls, a spokesman for a wireless industry group.

“There may be a time when the feature phone goes the way of the dinosaur, but it’s not going to be tomorrow,” said Walls, a spokesman for CTIA The Wireless Association. “More and more people want smartphones, but as long as a substantial percentage of consumers want a pretty standard device, I think suppliers will be producing that kind of equipment.”