If I'm going to just wear a shirt, I grab something from the closet with a pattern. Not a Hawaiian shirt, but a nice button up "office casual" shirt. The fashion trend has seen straight cut bottoms - no shirt tail - become popular and they look nice untucked. A tasteful pattern and good material will do more to disrupt the bulge. Besides, most folks AREN'T that observant, and its just a cell phone, anyway. . .
By the way, you might want to think about moving that revolver forward out of the small of your back. If you're worried about it "printing", nothing makes it obvious what it is as when you bend down to do down something with one there. Not to mention, its impossible to practice good handgun rentention in a SOB position, the draw is much harder (unless you're doublejointed . . . owww . . . that's hurts my shoulder to think about it), and i can't imagine how your butt feels after sitting on it all day long.