"important phenomena" is correct and can be used in written English.
For example, "Researchers have been studying the important phenomena of climate change for decades."
Some important phenomena are observed.
Several important phenomena are associated with e-commerce.
Other important phenomena, such as changes in clouds, are still too complex to model accurately.
These are important phenomena that help to explain why the poorest countries are not achieving economic progress.
In addition, the two most important phenomena that degrade soils, erosion and pollution, are discussed.
It also pays special attention to important phenomena such as adaptive trade-offs and leaf economics.
Shah has pioneered the use of data-mining techniques to capture sometimes elusive but medically important phenomena.
Thermal stresses are taken into consideration as important phenomena in many manufacturing processes and design applications.
Synchronization is one of the most important phenomena in coupled oscillators.
Two important phenomena may occur in the flow of particle suspensions.
These equations describe important phenomena in Physics and Engineering, being also subject to control issues.
