How do I get cbs live on my iPhone through my cable tv provider

Additionally, you may be able to sign in to the CBS app with your cable tv provider credentials, if they support this authentication (varies by provider). This sign-in may be automatic for TV providers in the Single Sign-On or Zero Sign-On program.

Sign in with your TV provider on your iPhone, iPad, or iPod touch - Apple Support

TV providers that let you sign in on your iPhone, iPad, or Apple TV - Apple Support

Apps that let you sign in with your TV provider on your iPhone, iPad, or Apple TV - Apple Support

You will have to see if they provide an app for live tv for the iPhone. Contact your cable provider.