According to the University of Texas
The researchers found that participants with their phones in another room significantly outperformed those with their phones on the desk, and they also slightly outperformed those participants who had kept their phones in a pocket or bag.
The findings suggest that the mere presence of one’s smartphone reduces available cognitive capacity and impairs cognitive functioning, even though people feel they’re giving their full attention and focus to the task at hand.
it didn’t matter whether a person’s smartphone was turned on or off, or whether it was lying face up or face down on a desk. Having a smartphone within sight or within easy reach reduces a person’s ability to focus and perform tasks because part of their brain is actively working to not pick up or use the phone.
“It’s not that participants were distracted because they were getting notifications on their phones,” said Ward. “The mere presence of their smartphone was enough to reduce their cognitive capacity.”