"Demand for Samsung's flagship Galaxy S10 started to weaken during the quarter, however, indicating that achieving growth in 2019 as a whole will be a challenge," said Anshul Gupta, senior research director at Gartner.
Global sales of smartphones to end-users declined 1.7% in the second quarter, totaling 368 million units.
"Demand for high-end smartphones has slowed at a greater rate than demand for midrange and low-end smartphones," Gupta added.
"To try to boost smartphone replacements, we've seen manufacturers bringing premium features such as multi-lens front/back cameras, bezel-less displays and large batteries from their flagship smartphones into lower-priced models," he noted.
Among the top five global smartphone vendors, Huawei and Samsung exhibited the strongest annual sales increases in the second quarter of 2019 — at 16.5% and 3.8%, respectively.
They accounted for more than a third of total smartphone sales globally.