I don't think that is an icon. It looks like it's the last four digits of the phone number, all stacked up on top of each other. It's going to be impossible to tell without seeing the original InDesign file.;
Look in the Story Editor with text selected to see if you can find the phone number. If you drew a box, delete it to see if the phone number shows up. Report back with your findings.
How did you create the box? This first one is in an anchored frame.
Using a Rule Above and Below would be quicker.
Drawing a box on top of the word Painting is most likely to cause problems.
How did you submit the ad? This has all the markings of someone opening a PDF in Illustrator.