Your smartphone does not have a radioactivity detector integrated, mate...

Whatever that App is, it's either a Joke app or it's a trojan horse created to make you play around while it infects your phone with a couple of virii

Or, you know, you're just trying to make a sensationalist click-bait and already knew this...

But benefit of the doubt and all that :)

EDIT: Apparently a smartphone CAN detect radiation. Several magazines have said so, at least.Though I haven't found an actual scientific article to confirm it...

https://academic.oup.com/rpd/article-abstract/168/3/314/2380247
This one says most of these Apps over or underestimate the values.

But you're still overreacting I'd say. Especially since GammaPix doesn't seem too reliable