Why am I forced to update my phone?!?

You are not forced to update your iPhone.

However, you will lose some security and features and over time there will be apps you can no longer use.

If you do not want to update your iPhone, go to:

Settings -> General -> Software Update -> Customize Automatic Updates.

Disable Download iOS Updates and Install iOS Updates.

However, I would recommend you to keep your iPhone up to date.

You are not forced. You can choose not to update. But updates contain security fixes and patches to make the device more secure, as well as new features and functions, so there's no reason not to want to update.