Three men were sentenced to several years in prison Tuesday after pleading guilty to charges related to a series of robberies that authorities said targeted District residents outside Metro stations and in neighborhoods such as Adams Morgan and L’Enfant Plaza.

Prosecutors said that since January, the men “canvassed the areas looking for targets of opportunity and teamed up to rob their victims.” They said the robbers sought people with expensive smartphones, particularly the iPhone 5s, and assaulted victims who resisted.

They then sold the stolen merchandise on the street or through what are called ecoATMs, automated recycling booths that give quick money for cellphones and have cropped up in suburban malls around Washington and Baltimore.

D.C. Police Chief Cathy L. Lanier has been an outspoken critic of the machines, telling a D.C. Council public safety committee that they help fuel the District’s high robbery numbers by offering another easy place to unload stolen electronic goods. The company’s owners have countered that security measures, such as requiring identification cards to be scanned in and forwarding lists of phones to law enforcement, offer adequate protection.

Stolen phones and laptop computers are also sold in other ways — to criminals or in stores and second-hand shops that can resell them cheaply. The Washington Post this week documented how a single laptop stolen from a D.C. school quickly ended up in an electronics store, got on eBay and was sold to an unsuspecting pastor in Louisiana.

In this latest case, the U.S. Attorney’s Office said the three men — Anthony J. Doggett, 21, of Suitland; Deasean Floyd, 19, of Oxon Hill; and Dominique C. Jones, 39, of the District — pleaded guilty in D.C. Superior Court to conspiracy to commit robbery, armed robbery, assault and other charges. They were sentenced to 13, eight and seven years in prison, respectively.

Authorities listed a series of robberies that occurred in January and February:

■ On Jan. 20, a woman getting into her car in the 1400 block of Pennsylvania Avenue SE was robbed of her purse and car keys. The robbers fled with the items, and one man returned to the area a week later and stole the woman’s car.

■ On Feb. 3, a man walking in the 1300 block of Q Street NW, in Logan Circle, was assaulted. After he collapsed on the ground, he was repeatedly punched in his head and body, then robbed of his iPhone and wallet. The phone was sold at an ecoATM at the Pentagon City Mall for $300.

■ On Feb. 5, prosecutors said one of the suspects took a gun, went to the area around 19th Street and Constitution Avenue, near Eastern Senior High School in Northeast, “and began to look for targets they could rob.” A young couple walking down the street was ordered to their knees, and a person who happened to be walking by also got held up at gunpoint. Prosecutors said the robbers met up in a nearby vacant house, where they wiped stolen phones of their memories.

■ On Feb. 10, a man was punched and robbed of his iPhone while standing on the platform of the L’Enfant Plaza Metro. When the victim tried to follow the men, prosectors said one punched him. The phone was sold at an ecoATM at the Pentagon City Mall for $300, prosecutors said.

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