Call forwarding

If you have a CDMA carrier, the options won't be shown on that screen. You need to contact the carrier. See the following from Manage incoming calls on iPhone - Apple Support

Set up call forwarding or call waiting (GSM)

1. Go to Settings  > Phone.
2. Tap any of the following:

• Call Forwarding:  appears in the status bar when call forwarding is on. You must be in range of the cellular network when you set iPhone to forward calls, or calls won’t be forwarded.
  • On models with Dual SIM, choose a line.
• Call Waiting: If you’re on a call and call waiting is turned off, incoming calls go directly to voicemail. Onmodels with Dual SIM, call waiting works only for incoming calls on thesame line, unless the other line has Wi-Fi calling enabled and a data connection is available. See Set up cellular service on iPhone.

For CDMA accounts, contact your carrier for information about enabling and using these features.

For information about conditional call forwarding (if available from your carrier) when the line is busy or not in service, contact your carrier for setup information.

Because either your cell provider doesn't offer that feature with the plan you are on or you have a profile from an employer that is blocking it. You also aren't showing Call Waiting or Show My Caller ID.