How do I allow certain contacts to call even when phones on silent

I want individual rings to come through even when phone is on silent. How is this done?

If the phone is truly on “Silent” (with the hardware switch) you can’t

However different Foci (Focuses ?) can be used to allow some callers to “ring-thru” on the 1st ring.

Allow or silence notifications for a Focus on iPhone – Apple Support (AU)

and

Change iPhone sounds and vibrations – Apple Support (AU)