I failed basic reading comprehension. The first sentence of the abstract clearly says "It has recently been shown that the mere presence of one’s own smartphone on the desk impairs working memory performance."

So while the presence of a smartphone does indeed seem to impair the working memory, they found "no overall effect of smartphone presence on short-term and prospective memory performance".

I think everyone here has a living experience of how smartphones reduce productivity. Even seeing one makes me want to check if I have new messages for example. Even if this one test did not replicate, I think its fair to say that there is a dark side of smartphone use

That's the case if you often get messages or notifications. I often get less than one message a day on my smartphone, so I can keep it on my desk without problems.

What about awareness/unhealthy attachment to the things it represents?