@misc15 , Welcome to the community!
Your modem is already switched to IPv4. You can set it to modem mode in the menu. If the menu is not visible, restart the modem.
Regarding your questions:
1. yes you have to plug the phone into the UPC modem
2. plug the UPC TV Box into the LAN port of your router After it is online, you have to open the port 2002 for the IP of your UPC TV Box to the outside
3. the internet is used for EPG, replay and the broadcasting rights
Greetings
Daniele