Q. It happens that sometimes I’ll look around during shacharis and see people whose Tefillin Shel Rosh is not in the proper position. What is the correct course of action when I see this? Should I quietly go up to them? Should I approach the gabbai about donating a mirror to the shul with the purpose of creating a “tefillin checking station”?

A. Horav Shlomo Miller’s Shlit’a opinion is that directly reprimanding or calling to attention individuals about their misplaced tefilin, especially if done repeatedly, may have the opposite effect and create discord. You also do not often see mirrors in the back of a shul. The reason may include that people will use them more for grooming themselves as they leave, something that may seem disrespectful to the inherent holiness of a shul.
The best course of action is to contact the Rabbi and remind him to teach in his talks and shiurim the importance of donning tefilin correctly with all the necessary details, stressing that one who does not do so has not complied with the mitzva and his brocho is in vain.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a