Turn on Silence Unknown Callers: Settings > Phone > Silence Unknown Callers
Use carrier spam-blocking features
Install a call-blocking app from the App Store
Block specific numbers: Phone > Recents > info icon > Block this Caller
Turn on Do Not Disturb or Focus mode
Report spam numbers to your carrier
Enable Live Voicemail if available
Keep iPhone updated to the latest iOS version
Avoid answering or calling back unknown numbers
Remove your number from marketing lists and robocall databases