Sales of Apple Inc.’s iPhone dropped for the first time in the fourth quarter last year, as the company lost market share in an arena that is increasingly being taken over by phone makers in developing countries.

In the final quarter of 2015, iPhone sales dropped 4.4%, cutting Apple’s AAPL, -3.43% market share to 17.7% from 20.4% in the same quarter of 2014, according to technology research company Gartner.

Overall, global smartphone sales for all manufacturers grew 9.7% quarter-on-quarter, the slowest rate of growth since 2008, Gartner found.

“Low-cost smartphones in emerging markets, and strong demand for premium smartphones, continued to be the driving factors,” said Anshul Gupta, research director at Gartner, in a statement. “An aggressive pricing from local and Chinese brands in the midrange and entry-level segments of emerging markets led to consumers upgrading more quickly to affordable smartphones.”

Analysts had expected a slowdown in iPhone sales in the company’s first quarter, partly due to muted enthusiasm over Apple’s most recent iPhone 6s model. Apple CEO Tim Cook also pointed to challenges related to the strong dollar DXY, -0.07% , as well as weakened currencies in Brazil, Russia and China, as the company brings in two-thirds of its revenue from overseas.

Apple’s own numbers do not match those provided by Gartner. The company said it sold 74.77 million iPhones in its fiscal first quarter ended Dec. 26, surpassing sales of 74.5 million units a year earlier. See: Apple reports slowing growth in iPhone sales

Read: Apple reaches peak iPhone, so what now?

The Gartner report also cited currency headwinds, and Gupta explained that emerging market currencies have put pressure on many sellers to set up operations overseas.

“Current market conditions are prompting some vendors to consider setting up manufacturing operations in India and Indonesia to avoid being hit by future unfavorable currency devaluations and high import taxes,” Gartner said.

Partly due to Apple’s iPhone struggles, as well as Google’s strong earnings, Google GOOGL, -3.34% GOOG, -3.48% surpassed Apple to become the world’s largest company by market value for a brief period this year.

In the worldwide smartphone space, Samsung Electronics Co. 005930, -0.33% , had the biggest individual market share for the fourth quarter at 20.7%, up from 19.9% a year ago. For the whole of 2015, however, its market share fell to 22.5% from 24.7%.

“For Samsung to stop falling sales of premium smartphones, it needs to introduce new flagship smartphones that can compete with iPhones and stop the churn to iOS devices,” said Gupta.

Chinese smartphone maker Huawei Technology Co. Ltd. 002502, +1.42% saw the biggest jump in the fourth quarter, with sales surging 53%.

Despite its slowing iPhone sales, Apple did see an uptick in market share for the full year, at 15.9% from 15.4% for the previous year.

— Caitlin Huston contributed to this article.