The phrase "to play a pivotal role" means to have an important and significant impact on something, often by being instrumental in bringing about change or influencing the outcome. Full definition
In terms playing a pivotal role in several art movements. (culturetype.com)
They also play a pivotal role in helping to shine a spotlight on our nation's leading private businesses. (events.grantthornton.ca)
At the same time, that is the saving grace of this long overdue film on a character who played the pivotal role in an incident that would come to define political scandals. (indianexpress.com)