iPhone has long been Apple's tablet product and main prize, but sales are beginning to decline. The company pushes digital subscriptions as it seeks new growth.
Apple is one of many US companies now struggling with rising Chinese consumer fear. China is an important market for Apple and other smartphone manufacturers, accounting for one-third of the industry's global handovers.
In other comments, Cook said the world was "facing more challenges than ever before."
"Climate change threatens our planet, poverty and inequality keep citizens and nations back from their potential, basic health care is out of reach for millions," he said.
"At the same time, we can have a healthy planet and a thriving economy. We can continue to lift millions of people out of poverty and we can give everyone a chance to learn and thrive. all work hand in hand, government, academic institutions and companies like Apple, "Cook said.