You may want to read the paper Brain Drain: The Mere Presence of One’s Own Smartphone Reduces Available Cognitive Capacity, by A. F. Ward et al., published in Journal of the Association for Consumer Research (April 2017). DOI: 10.1086/691462.
Based on their experiments, the authors claim that “the mere presence of one’s smartphone may reduce available cognitive capacity and impair cognitive functioning, even when consumers are successful at remaining focused on the task at hand.” The “mere presence” means that users “do not interact with or receive notifications from their phones.”
The authors illustrate their findings with the figure below. It shows that, when it comes to “working memory capacity” and “fluid intelligence,” you are better off if you place your smartphone further away from yourself (a bag is better than a desk, and another room is still better).
If you’d like to learn about so-called ambient displays, which allow you to receive information without smartphones or other screen-based computers, consider taking our course AKIR (in Polish).