Connecting to OpenVPN Using the piVPN Server on Raspberry Pi
This video shows how to install the piVPN server and configure it in RaspbianOS on the Raspberry Pi. Mobile devices will have to have OpenVPN apps (mobile or otherwise) installed and then you can import the generated OVPN file for each mobile device account into OpenVPN GUI to make the connection.
piVPN Project Website: http://www.pivpn.io