If you were on approved breaks and you were using your phone when and as allowed by your employer, that is between you and your employer. Of course if that had been the case you would still be employed. Going on a limb these were not sent while you were on an approved bathroom break or otherwise off duty. If you weren't supervising the students that is a huge deal. That kind of thing gets reported often and gets taken very seriously, just as any other report from the public, parents, fellow staff members, students, etc. of employees potentially being negligent in their duties. The school investigates and if they find merit, acts accordingly. I'm truly baffled why you think that someone wouldn't be allowed to report this. The email address used to make the report and when that report is made is of absolutely zero consequence as far as your guilt or innocence.