In brief: Despite new technologies such as folding phones, the smartphone market is predicted to decline by 3 percent this year. That's the view of analyst firm CCS Insight, which has revised its initial prediction of 2 billion sales through 2019 down to 1.8 billion.

The slump has been blamed on familiar reasons: many smartphone owners are keeping their devices longer before upgrading; the weaker Chinese economy is having a negative effect; more people are choosing second-hand options, and flagship prices are skyrocketing.

In Western Europe, where sales have fallen 23 percent over the last six years, 35 percent of consumers said they would be keeping their current handset longer than their previous device. Only 13 percent of people said they would be upgrading faster than before.

"This trend has slammed the brakes on Western European markets, and we believe similar dynamics are now having a dramatic impact in the US, where we forecast sales will drop 9 percent in 2019," said Marina Koytcheva, VP of forecasting.

CCS Insight has downgraded expectations in virtually every market. China is predicted to fall by nine percent, and while India is heading in the right direction, its sales are increasing by just five percent. The country is expected to show improved growth in the future, however, with sales reaching 400 million by 2023.

As many flagships are now priced over $1000, more consumers are cautious when it comes to buying a brand-new device, with the second-hand market becoming more of an appealing prospect.

One bright spot is 5G. While the technology might be in its infancy, CCS believes 220 million 5G-compatible phones will be sold next year. By 2023, that number is expected to have risen to 930 million, representing almost half of all phone sales.

"History has shown that the introduction of a new 'G' always helps to energize demand for new phones, and 5G will be no exception," said Koytcheva.