All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is disliked for a praying person to look at the messages in his cell phone as this distracts him from the prayer. Ibn Qudaamah said in Al-Mughni: “It is disliked for a person to look at what distracts him or look in a book as ‘Aa’ishah narrated that the Prophet prayed on a Khameesah (a garment with patterns on it), then (when he finished the prayer) he said: "The pattern on this (Khameesah) distracted me. Take it to Abu Jahm ibn Huthayfah and bring me his Anbijaaniyyah (a woolen garment without patterns)." [Al-Bukhari, Muslim and Abu Daawood]
Also, the Prophet said to ‘Aa’ishah : “Take this curtain of yours away from me as the images on it continue to distract me from the prayer.” [Al-Bukhari]
For more benefit, please refer to Fataawa 128482 and 92210.
Moreover, taking out the cell phone to read the message or to know who the caller was, if this requires much movement that is more than usual, then this may invalidate the prayer.
For more benefit, please refer to Fatwa 186483.
Allaah Knows best.