What is the ruling on not turning off a mobile phone in the mosque during prayer, and what is the effect of that on the devotion of the worshipers?

The phone must be switched off when entering the mosque as an act of reverence for the sacred ordinances of Allah and to avoid disturbing worshipers. The Imam and others should remind people of this. A ringing mobile phone is not an excuse for failing to attend congregational prayer in the mosque, which is obligatory for any able man who hears the call.