Use your phone’s built-in call forwarding to forward calls to the person’s voicemail number, if available
Dial the voicemail access number directly, if you know it and it is supported by the carrier
Turn on Do Not Disturb or Focus mode and allow calls from no one, so calls go to voicemail
Put the phone in Airplane Mode or power it off so calls are sent to voicemail
Block the caller’s number on your phone, if you want their calls to go straight to voicemail
Ask the carrier for voicemail routing options or call handling features
Use a third-party call management app that supports voicemail routing, if permitted by your carrier
Leave the phone unanswered until it rings out, if your goal is for the call to go to voicemail