Several times using this at bed time but during using when i sleeped its my under body whole night is it safe or its cause any issue in future?
You should never have your phone in bed with you, unless you are using it. Any cell/smart phone that gets covered up runs a high risk of overheating and catching fire!!
Tell that to the makers of the "Sleep as android" and other sleep cycle tracking apps; they recommend putting the phone on your mattress so the accelerometers on the phone can pick up movement and track your sleep cycles.