Global smartphone sales took a tumble this quarter, largely because the Chinese market is saturated, so people there aren't buying as many high-end phones.

That took a small toll on the Android operating system, though Google's OS is still by far the most popular, according to data from Gartner.

Overall smartphone sales, meanwhile, also grew 13.5 percent year over year, but that's the slowest growth rate since 2013.

"China has reached saturation—its phone market is essentially driven by replacement, with fewer first-time buyers," Anshul Gupta, research director at Gartner, said in a statement. "Beyond the lower-end phone segment, the appeal of premium smartphones will be key for vendors to attract upgrades and to maintain or grow their market share in China."

Samsung rolled out its latest high-end smartphones earlier this year, the Galaxy S6 and Galaxy S6 . But it still struggled to compete against Apple's larger iPhone lineup, Gartner said.

Samsung was the No. 1 smartphone vendor during the second quarter with 21.9 percent of the market, but that was down from 26.2 percent during the same time period last year. It sold approximately 72 million smartphones in Q2 but 76 million last year.

Apple, meanwhile, increased its global market share from 12.2 percent to 14.6 percent with sales of 48 million iPhones. "Apple recorded strong iPhone replacements in both emerging and mature markets — and particularly in China," Gartner said. "Total iPhone sales in China grew 68 percent to 11.9 million units."

Rounding out the top five smartphone vendors were Huawei (7.8 percent), Lenovo (5 percent), and Xiaomi (4.9 percent).

When it comes to mobile operating systems, meanwhile, Android was still No. 1 with 82.2 percent of the market, but Google's OS had its challenges this quarter, reporting its lowest year-over-year growth of 11 percent, Gupta said.

Overall, Android and iOS dominate 96.8 percent of the world's smartphones. Windows dropped from 2.8 percent to 2.5 percent as "Microsoft continued to struggle to generate wider demand for Windows Phone devices — even at the lower end," Gartner said.

Redmond has since launched Windows 10 and is rumored to be holding an October event that will showcase new high-end Lumia devices. But "in light of Microsoft's recent cuts in its mobile hardware business, we'll await signs of its long-term commitment in the smartphone market," Gupta said.