There are so many logos with stars everywhere (not only in Germany - http://www.stern.de/2) but to say that the logos resemble each other or one gets confused would be an exaggeration.
Stern isn’t in the smartphone industry, so there’s no problem there. The problems arise when 2 companies in similar sectors have similar brands.
For example, Sky TV recently took Microsoft to court over the SkyDrive name. Microsoft was ordered to change the name because they both provide online services (even though the nature of those services are very different).
So, because the Fairphone star logo is similar to that of a company in a similar industry, there is sufficient need for change. For an organisation the size of Fairphone, it’s better to be safe than sorry.
That said, I don’t think the current logo is distinctive or modern enough, nor does it communicate fairphone ethics in any way.