What is the ruling regarding an Imam who takes out his mobile phone during congregational prayer to see who is calling?

Humility (khushu') is the spirit and essence of prayer. For an Imam whose prayer distracts him from its purpose, which is humility, what he is doing is an even greater distraction. The worshipper should turn his heart to his Lord, for indeed, there is engagement in prayer. This action by the Imam does not invalidate the prayer if it is minor, but it is disliked because it distracts from the prayer without need. The Imam should be a role model for those praying behind him in being diligent about the manners of prayer and perfecting humility within it.