Hello M.chakur,
Thanks for using Apple Support Communities.
From your post I see you are concerned about the temperature of your iPhone 5s. The article below explains more about why the temperature of an iPhone can increase, and how to keep the device within its acceptable temperature.
When using the device or charging the battery, it is normal for it to get warm. The exterior of
the device functions as a cooling surface that transfers heat from inside the device to the cooler air outside.
Higher ambient temperature conditions and activities that may cause the device to alter performance and behavior include:
- Leaving the device in a car on a hot day.
- Leaving the device in direct sunlight for an extended period of time.
- Using certain features in hot conditions or direct sunlight for an extended period of time, such as GPS tracking or navigation in a car, or playing a graphics-intensive game.
iOS devices: Keeping device within acceptable operating temperatures
http://support.apple.com/kb/HT2101
Take care,
Alex H.