A new survey finds nearly 20% of full-time employees are productive fewer than five hours a day. The cause of that lost productivity? Smartphones.

We have been here before. First, employers blamed the Web for lost productivity. They responded by blocking access to the Web, only to open it later when they realized it actually contained work-related content. Later, social media was the culprit. Businesses responded, predictably, by blocking social media sites. Now, a quarter of companies are banning personal calls and cell phone use.

Nearly half of employers insist smartphone distractions have compromised work quality, lowered morale as other employees are forced to pick up the slack, negatively impacted relationships between employees and bosses, and led to missed deadlines.

Only 10% of employees with smartphones agreed that their productivity is dropping because of their phone use, though 66% said they use their phones several times during the workday.

While some productivity may suffer, I suspect the reality isn’t far from the reality of Web and social media use. Looking at the amount of time employees spent on non-work-related websites, Websense calculated a multi-billion-dollar loss in productivity. The problem with its calculation is that it had nothing to do with productivity. How many extra hours were those employees working in order to complete their tasks? How much work were they doing away from the office? It says something that, at the same time Websense made its case that productivity was suffering, the U.S. Department of Labor released statistics revealing a rise in U.S. worker productivity.

I suspect the same thing is happening here: Bosses see workers on their phones and assume that must mean they’re not getting their jobs done. To be sure, there have always been employees who will waste time. Those using smartphones to do it today probably used crossword puzzles or other time-wasters before digital tools were available. To paint everybody with that brush, though, is just wrong.

Smartphones are the gateway to the Net, where work gets done

Just how wrong becomes clear when you look at new data from the Pew Research Center about how employees use social media at work. The data is relevant since other research shows most social media activities these days happen on smartphones. According to the Pew report, 24% of workers use social media to make or support professional connections, which more often than not pay off for the company. Twenty percent get information that helps solve problems at work, 17% build or strengthen personal relationships with coworkers, another 17% learn about someone they work with, 12% ask work-related questions of people outside the organization and 12% ask work-related questions of people inside the organization.

As for the top result, 34% use social media to take a mental break from work. While that may seem like a time-waster to a boss who doesn’t know any better, the fact is that mental breaks improve productivity. A University of Melbourne study, for instance, found that workers who had web access were 9% more productive than those who couldn’t. They took short breaks while doing their work, and “the distractions kept them sharper than the folks who had no choice but to keep on task.”

The lost productivity myth actually produces even worse results than you might expect. It turns out that companies with social media policies are less likely to use it to solve work problems! A quarter of workers at companies without workplace policies use social media to solve problems at work while only 16% of those working at companies with restrictive policies take advantage of the resource. Fewer employees at companies with policies take mental breaks from work, which (according to research) lowers their productivity.

It’s also worth noting that smartphones are also increasingly the way employees tap into enterprise social networks, company intranets, and other work-related resources, many of which are housed in the cloud. A ban just keeps employees from the resources the company wants them to use.

Sweeping bans are counterproductive

Ultimately, studies like the Careerbuilder survey lead companies to make kneejerk decisions that ultimately do more harm than good. Most workers believe social media ultimately helps their job performance. The remedy is to measure real productivity: Is the work getting done? Is it getting done on time? Does it meet quality requirements?

Second, bosses need to manage by exception. The vast majority of workers won’t let their smartphone activities get in the way of doing a good job. After all, they want bonuses, promotions, raises, recognition, and the other benefits, intrinsic and extrinsic, of doing good work. Deal with the minority of employees whose performance is suffering and leave everyone else alone. It won’t build employee engagement if employees who manage to use their phones and do a great job are punished for the behaviors of a few others, will it?

Third, figure out how smartphone use (which has become the primary means of being online) benefits the organization and promote those behaviors. Employees who tap into peer networks online solve problems considerably faster than those who don’t. A quarter of employees say they never use the Internet for work-related tasks. Now that’s  a contributor to lowered productivity!