Open the Settings app
Tap Phone
Tap Call Blocking & Identification
Turn on the switch for Silence Unknown Callers
Open Settings
Tap Phone
Tap Call Blocking & Identification
Tap Block Contact
Open the Phone app
Go to Recents
Tap the info icon next to the number
Tap Block this Caller
Enable blocking for spam robocalls: Settings → Phone → Call Blocking & Identification (toggle on Silence Unknown Callers)
Report spam calls from the Phone app: open Recents → tap the number’s info icon → select Report Junk (if available)
Use a carrier spam-blocking feature: check your carrier app or support page for spam call blocking options