Unwanted outgoing phone calls Occasionally, when I flip the lid of my phone and put it on the table, the phone calls the primary number of the contact with which I communicated last (by phone or text message).

I suspect that some button has this function under certain circumstances, but I am not able to reproduce this call back voluntarily.

Does anyone know what happens to me? And maybe how to deactivate this hidden callback feature.

I have a Samsung Galaxy S5 mini. 

Edit: According to the answer I received, I moved the icon of the phone app, so that it would be impossible to tap it three times by closing the lid. But this didn't change the problem. The annoying unwanted outgoing calls still persist.
Depending on where the phone app icon is on your screen, it’s can be very easy to tap it twice. Once to start the phone app and a second time to select the phone instead of contacts, call logs or groups. One more time at the same position will dial the last number in the call log. This is most likely what’s going on try it as see. Just tap that the little green phone icon a couple of times.