According to the IDC Worldwide Quarterly Mobile Phone Tracker, global shipments will fall by 0.7 % to 1.455 billion units, compared to 1.465 billion in 2017.
However, a small rise in shipments is seen in the second half of 2018, with volumes rising by 1.1% compared to the second half of 2017. That volume is expected to reach 1.646 billion units by 2022.
The company said large-screen smartphones — 5.5 inches and larger — would lead shipments with 841.6 million units (64.7%) shipped in 2018, making up nearly two-thirds of all shipments. The figures for 2017 were 623.2 million units of 42.5%.
The company said as Chinese brands like OPPO, Huawei, vivo and Xiaomi expanded their international presence, the focus on large screens and aspect ratios would be across their entire range.
"With two out of three new iPhones expected to be larger than six inches, Apple will not be left behind in the 2018 race for increased screen real estate," said Melissa Chau, associate research director with IDC's Worldwide Quarterly Mobile Device Trackers.
"You could say the term 'phablet' is becoming less relevant now that most smartphones will ship with larger screens, and when folding screens start coming into play in the medium term, this screen trend will evolve in new directions."
IDC said the Chinese market was showing signs of recovery and while it was expected to be down 6.3% this year - a little worse than the 2017 fall - that would be due to a bad first half that saw smartphone shipments fall by 11%.
The second half of 2018 is expected to limit that fall to 2% before growth was experienced in 2019.
“We still believe the smartphone market has some healthy growth in the years to come, although finding and competing in those markets and segments is increasingly more challenging," said Ryan Reith, program vice-president with IDC's Worldwide Mobile Device Trackers.
"With the US-China trade tariffs changing and unfolding daily it is hard to pinpoint what the exact impact on the market will be, but for the time being OEMs are pushing forward with important initiatives that include the previously mentioned traction around bigger and better displays.
"But the industry also has 5G knocking at its doors, and many OEMs, retailers, telcos, and supply chain partners will be working diligently to ensure consumers see the need to upgrade when products and services are readily available."
Graphics: courtesy IDC