My mobile phone sometimes turns off automatically when I send a text message or make a call. What's going on here?

1) is generally a battery problem. After a period of use, the internal resistance of lithium batteries will become larger. Although fully charged, the no-load voltage is not low, and there is no problem in standby.

However, when making a phone call, the current becomes larger, and the voltage applied to the mobile phone will decrease, so it will automatically turn off.

2) Another possibility is that the mobile phone will automatically turn off when it fails, resulting in excessive working current.

The first situation is the most common. You can try a new battery first. If it still can't be solved, you can only find maintenance personnel to check whether the working current of the mobile phone is normal.