Wa'alaikum Assalam Warahmatullahi Wabarakatuh (peace be upon you and mercy and blessings of Allah),certainly recitation the Holy Quran from Al-Musshaf is better than reciting it by heart,because recitation from the Book combines two worships,worship of the recitation, and and the worship of looking at the Holy Quran, and recitation from the mobile phone as well the computer combines between the two worships looking and recitation