A rising number of influential voices are sounding the alarm about the dangers of smartphone technology, as major investors in Apple urge the company to address the public health crisis of youth phone addiction.

The Wall Street Journal reported this week that Jana Partners LLC and the California State Teachers’ Retirement System, also known as Calstrs, are leveraging their influence with Apple. Together these two large shareholders, which control approximately $2 billion in company stock, submitted a letter on Saturday stressing that Apple needs to build new software tools to assist parents in limiting phone use. The letter also called on the company to further research how excessive use of smartphones impacts mental health.

“Apple can play a defining role in signaling to the industry that paying special attention to the health and development of the next generation is both good business and the right thing to do,” the shareholders’ letter reads.

“There is a developing consensus around the world including Silicon Valley that the potential long-term consequences of new technologies need to be factored in at the outset, and no company can outsource that responsibility.”

The iPhone is considered Apple’s “backbone,” the WSJ noted. The company turned a $48.35 billion profit in its most recent fiscal year, and the iPhone helped turn the business into the world’s largest publicly listed company by market value. Apple’s stock grew by 50 percent in the past year, and approximately 86 million Americans older than 13 now have an iPhone.

“The investors believe that Apple’s highflying stock could be…