This is a common misunderstanding among the Muslim to decide whether they should keep the mobile phones, those mobile phones in which we store Quranic verses, along with them or not while going to the toilet.
On the issue, one asked to Sheikh Abdullah al Mutlaq (who is the Islamic theologian in Saudi Arabia) who replied that there is no issue of carrying the mobile phone while going in the toilet.
Mr. Sheikh added that this was like memorizing the holy Quran and then thinking whether to keep the brain with or not while visiting in the toilet.