The Pew Research Center found some 64 percent of American adults owned a smartphone as of the survey last year, almost double the percentage of 2011.
And 15 percent of those surveyed said they had a smartphone and "limited" access to the Internet from other sources. Ten percent in the survey said they had no broadband Internet at home.
In sum, the figures mean around one out of 14 Americans is "smartphone dependent," with no high-speed Internet at home and little access elsewhere, Pew said.
A large number of these "smartphone-dependent" users are young adults: some 15 percent of those in the 18-29 age group fit that description, the survey found. Those with lower incomes and lower educational attainment were also more likely to depend on their handsets.
"Compared with smartphone owners who are less reliant on their mobile devices, these smartphone-dependent users are less likely to own some other type of computing device, less likely to have a bank account, less likely to be covered by health insurance and more likely to rent or to live with a friend or family member rather than own their own home," the Pew report said.
But because these people have lower incomes, many have had trouble paying their smartphone bills, according to Pew.
Around 23 percent of smartphone owners said they had to cancel or suspend their service for financial reasons, and 15 percent said they often reach the maximum amount of data allowed on their plan.
"The connections to online resources that smartphones facilitate are often most tenuous for those users who rely on those connections the most," said Aaron Smith, a Pew researcher.
"A substantial minority of Americans indicate that their phone plays a central role in their ability to access digital services and online content, but for many users, this access may not be available when they need it due to financial stresses or technical constraints."
Although 93 percent said their smartphone is useful, less than half 46 percent claimed they "could live without" their device, and 54 percent said it was "not always needed."
Wide range of uses
While smartphone users access the Internet on their handsets for a variety of things, low-income and smartphone-dependent users are especially likely to use their phone for work, or to help find a job.
Overall, the study found 62 percent of smartphone owners have used their phone to look up information about a health condition, and 57 percent for online banking.
More than four in 10 used their phone to look up real estate listings or other information about a place to live, or to find information about a job. And 18 percent used their phone to submit a job application.
More than two thirds of smartphone owners said they used the devices to follow breaking news, with 33 percent saying that they do this "frequently."
And 67 percent said they used their phones at least occasionally as GPS devices while driving, with 31 percent using this feature often.
The report is based on telephone surveys conducted in December 2014 among 2,002 adults, with some data from surveys in October and November. The margin of error was estimated at 2.5 percentage points.