How can I arrange static IP for client?

[Mr. Jingles]

Hello  :)

I now have pfSense be a OpenVPN server for my smartphone client, while abroad.

I would want to lock it all down as much as possible, so in the Firewall/OpenVPN tab I would like to add a rule for the static IP of my Smartphone (based on MAC). But in DHCP-server I don't have a tab for the OpenVPN-server.

Would there be any other way to set this up?

Like as I asked here (https://forum.pfsense.org/index.php?topic=130914.0):

Is this way of setting OpenVPN better: https://forums.servethehome.com/index.php?threads/pfsense-site-to-site-vpn-connected-but-traffic-not-passing.5534/

Thank you :)