All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Mobile phones and other electronic devices in which the Quran is stored are not considered as a Mus-haf (Quran book) and the ruling of a Quran does not apply to them with regard to the obligation of being in a state of ablution to touch it and being disliked to enter the toilet with it and so forth. However, if the verses of the Quran are displayed on the screen of the phone, it is disliked to enter the toilet with it.
As regards whether or not it is a sin if the phone falls down when the verses of the Quran appear on the screen, if it is an accident and it did not happen deliberately, then one is not sinful. Allaah Says (which means): {And there is no sin on you concerning that in which you made a mistake, except in regard to what your hearts deliberately intend. And Allaah is ever Oft-Forgiving, Most Merciful.}[Quran 33:5]
For more details, please refer to Fatwa 90212 on phones which contain the Quran.
Allaah Knows best.