My Iphone gets warm and deletes all the contacts (phone numbers and names)?

This has happened 4-5 times, otherwise its functions are normal. What may this be?

You MAY have a defective battery. Take it to apple and they'll take a look at it. Beware, it gets very crowded, so call them and make an appointment. Also, if you got your cell phone less than a year ago, you will get it fixed for free or a new one if they can't fix it.