If you are only concerned for cancer risk then till date there are no evidence to suggest any increased risk because if cellphone uses , as mobile phone emits non ionising radiation . But keeping mobile on chest is harmful for your health in number of ways . PLEASE AVOUD THIS .

Mobile phones work on the principles of microwave radiation. They're non-ionizing in nature ( they don't cause DNA damage). Therefore the risk of cancer developing out of mobile phones is negligible. Keep in mind though, mobile signals can interfere with some pacemakers so those who have one implanted ; better to keep it far from your body whenever possible. Also, keep your mobile phone switched off when in flight ;)

Currently  there is no evidence to link the non ionizing radiation emitted by mobile phones to cancer. The Federal Communications Commission (FCC) concludes that currently no scientific evidence establishes a definite link between wireless device use and cancer or other illnesses. In 2015, the European Commission Scientific Committee on Emerging and Newly Identified Health Risks concluded that, overall, the epidemiologic studies on cell phone radiofrequency electromagnetic radiation exposure do not show an increased risk of brain tumors or of other cancers of the head and neck region and malignancies of other sites.