phone keeps restarting

The first thing I would try is reset it to factory settings but don’t restore, rather set it up as a new phone. If the problem goes away, that likely indicates something in your backup causing this, most likely a corrupt app or app data. From that point you can start downloading apps one by one until you find the app causing this. If it is corrupt app data, just not restoring will prevent that. If that process does not work or if the problem exists when the phone is reset, your best course of action is take it to Apple.

 Here are some possible ways to fix it: https://www.howtoisolve.com/iphone-x-keeps-restarting-by-itself/

You can try these methods:

1 Force Restart Your iPhone

1) Quickly press and release the volume up button.

2) Quickly press and release the volume down button.

3) Press and keep holding the side button until the screen turns off and then turns back on. Then you can release the side button when the Apple logo appears. After that, your iPhone will restart automatically.

2.Use iOS repair tool to Fix Without Data Loss and also easy.

3. Using iTunes To Restore iPhone

1) Simply connect your iPhone to a computer and launch iTunes.

2) A pop-up window will appear not long after iTunes finish detecting a problem with your iPhone. Just hit "Restore".

3) If the pop-up didn't show up, you can click on "Summary" and then "Restore iPhone" to restore your iPhone manually.

For More details: why does my iphone keep restarting 

@conysdf You responded to a 3 year old thread. Not likely the OP is still looking for a solution. Closing this thread.