Q: Problems with my iphone 6s plus

Make sure you have rotation enabled.

If the screen doesn't rotate on your iPhone, iPad, or iPod touch - Apple Support

Take a look at this article:

Get help with hardware features on your iPhone, iPad, and iPod touch - Apple Support

You can also try these steps: This won't delete your data stored on the phone.

• Press and hold the Sleep/Wake button
• Press and hold on the Home button
• Keep holding both buttons until the display turns off and back on with Apple logo on it.

Alternatively, you may go to Settings - General - Reset - Reset All Settings

https://support.apple.com/en-us/HT201559

If this does not help, restore your device to factory settings. Note that this will erase the data from your device.

Take a look this Apple Support article: Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support.

Take it back to place of purchase for repair/replacement if there has been no user damage.

Cheers

Pete