Is it permissible to pray next to a person who is holding a mobile phone with indecent pictures on it in the company mosque?

It is not permissible to keep forbidden images on a mobile phone or to look at them, based on the Almighty's saying: "Tell the believing men to reduce [some] of their vision and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do." The owner of these images must repent and delete them. You should advise him gently and wisely, in accordance with the Almighty's saying: "And enjoin what is right and forbid what is wrong." As for praying with him in the mosque, it is permissible. His possession of the images does not invalidate the prayer or prevent congregational prayer.