Tefillin
Question
Do I have to fast if I drop my tefillin?
Answer
Shalom!
Thank you for your question.
One who drops his tefillin should fast. The fast serves to atone for not having been careful when handling the tefillin . The fast is only required if the tefillin were completely exposed. One who drops his tefillin while putting them on for Shacharit should consider fasting that same day, if one did not yet eat or drink anything that morning. If one did already eat or drink something that morning, then one should fast the next day and be mekabel the fast, during Mincha. Some one who Cant fast should redeem his fast by giving the amount of money he would spend on food a day to tsedaka.
Someone who the fast will disturb his learning like a Bachur Yeshivah and an Avreich should not fast but rather give tsedaka (the amount of money that one would spend on food in a day,). Bachurim should learn the Full sedarim of the Yeshivah be'taanit dibbur and Avreichim should also learn Betaanit dibbur, and at the next Ta'anit Tsibur, they should have in mind that the fast is also for this.
If they were merely covered with a protective covering, such as the plastic casings that are commonly placed on the tefillin in order to protect them, then one is not required to fast rather one should give a peruttah to tsedaka, as a form of atonement for the tefillin having fallen to the floor.
If the Teffilin were in the Teffiliin bag, then one doesn't need to give a perutah to tsedaka.
Source
Azamroh Lishmech issue #275
Halacha Pesukah - Teffilin Page 174