IDC has published a report with forecast projections for global smartphone shipments in 2018 and 2022. The research company expects a drop of 3% in 2018 followed by a small increase in 2019 that will carry on through to 2022. The total units shipped for 2018 is estimated at 1.42 billion while the 2022 estimate is put at 1.57 billion. Android should maintain a comfortable lead in terms of platform used.
https://www.notebookcheck.net/IDC-forecasts-smartphone-shipment-growth-in-2019-and-through-2022.376861.0.html