Smartphones have been around for over ten years, so you'd think that most managers would have learned how to use them effectively. You'd think wrong, though, because many bosses still make these three dumb mistakes on daily basis:

1. Phubbing employees

Phubbing (looking at your phone while you're having a face-to-face conversation) is rude under any circumstances. When a manager does it to an employee, it communicates that the employee is less important to the manager than whatever is on the phone. While this might very well be true, showing employees that you consider them unimportant will NOT inspire them to do their best work. As the Washington Post put it:

"Researchers found that boss phubbing negatively impacts employees' trust in their supervisor, which in turn negatively affects the employee's feeling that their work is meaningful, that they have the necessary resources to do their job, and that they are in a safe working environment. All this in turn leads to decreased employee engagement and productivity."

2. Texting or emailing "feedback"

The purpose of criticism (or "feedback" if you prefer) is to improve employee behavior. If not delivered carefully (i.e. accompanied by praise and coaching), most employees will focus on the sting of criticism ("Argh! My boss thinks I'm an idiot!") rather than its intent.

That's especially true with texting, where the criticism is likely to be terse and the capacity for praise and coaching scant. Giving criticism by email is even worse with email, according the Harvard Business Review:

"Daniel Goleman calls a natural 'negativity bias' toward email... If the sender feels positive about an email, then the receiver usually feels neutral. And if the sender feels neutral about the message, then the receiver typically feels negative about it. In other words, email really is like kryptonite: it's as if every message you send gets automatically downgraded a few positivity notches by the time someone else receives it."

3. Using devices at your own meeting

Business meetings are inherently expensive because they involve multiple people. It is therefore a manager's job to make certain that meetings are productive, which by definition means short and to the point. If you're so bored by your own meeting that you're surfing the Web, answering emails, or checking your messages, you are showing your employees everyone that time isn't valuable and that you're a bit clueless.

BTW, a "no devices during meetings; hard copy notes only" policy will give any organization a huge productivity boost. As Forbes recently pointed out: , taking notes by hand increases retention and increases productivity:

"Recent studies provide evidence that the physical process of writing notes down versus typing them improves memory and your ability to answer conceptual questions... [In addition,] meeting participants who jump between email replies and engaging in the meeting are unable to focus closely on either task. They are either tuned out of the meeting, or not paying close attention to that email they are about to send."