Research shows that having your smartphone nearby takes a toll on your thinking:
Our research suggests that, in a way, the mere presence of our smartphones is like the sound of our names — they are constantly calling to us, exerting a gravitational pull on our attention. If you have ever felt a “phantom buzz” you inherently know this. Attempts to block or resist this pull takes a toll by impairing our cognitive abilities. In a poignant twist, then, this means that when we are successful at resisting the urge to attend to our smartphones, we may actually be undermining our own cognitive performance.
The best thing you can do is schedule time during your day where you put your smartphone in another room. (via Rian van der Merwe)