A cell phone that turns itself off can't make or receive calls, and so isn't particularly useful. There's not enough market for such a device, so companies don't make them.
There are phones that can be set to turn themselves off a specific time. A lot of smart phones should have this capabilities. I know that Blackberry phones have this feature to help conserve battery life. However I don't know of any of the normal phones that come with this feature included.
Some times your phone get grubby so it cause turn off itself,for that take out your battery and clean the posts on it with some rubbing alcohol or qtip An eraser can also be used for that. Otherwise try cell phone reset it is better to take a back up of the data of your phone hope it works.