What is the ruling on the prayer of someone who stands behind the Imam and plays with his phone, then when the Imam bows, he says "Allahu Akbar" and bows with him, knowing that he was not late for the prayer for any reason and did not recite Al-Fatihah?

The majority of scholars hold that whoever catches the Imam in bowing (rukūʿ) has caught the rakʿah, citing the Prophet's (peace be upon him) saying: "Whoever catches the bowing has caught the rakʿah." However, the Zahiris disagreed with this, as did Imam al-Bukhari. Some jurists believe that this rakʿah is not valid if the follower deliberately delays joining the Imam without an excuse until the Imam bows, because this action is not sound and causes him to miss the pillars of standing and reciting Al-Fatihah.