2D Game rotates on the android mobile phone

I created a 2D game for the mobile phone that should only be playable vertically, but when I turn/rotate the mobile phone, the game switches to horizontal. How do I set the game in untiy that it just stays vertical when i play in on my phone.

It’s in the player options. See build dialog.
https://docs.unity3d.com/2018.2/Documentation/Manual/class-PlayerSettings.html