Does the reward for reading or memorizing the Qur'an from a mobile phone decrease compared to reading it from the Mushaf?

The best approach to reading the Quran is to do whatever increases humility and devotion (khushu'), whether that is reading from memory, from a physical Mushaf, or from a mobile phone. The entire focus is on the presence of the heart and contemplation (tadabbur).

Imam An-Nawawi said: "Reading the Quran from the Mushaf is better than reading it from memory. This is what our companions said, and it is well-known among the Salaf... However, if reading from memory brings more contemplation, reflection, and presence of heart and sight to the reader than reading from the Mushaf, then reading from memory is better. If they are equal, then reading from the Mushaf is better. This is what the Salaf intended."

Ibn Baz was asked about the difference between reading from the Mushaf or by heart, and he replied: "I do not know of any evidence that differentiates between reading from the Mushaf or reading by heart. What is prescribed is contemplation and the presence of the heart... If reading by heart makes one's heart more humble and closer to contemplating the Quran, then it is better. And if reading from the Mushaf makes one's heart more humble and more complete in its contemplation, then it is better."

Therefore, reading from a mobile phone with humility and contemplation does not diminish the reward compared to reading from a Mushaf.