This is by far the easiest option, you can use for instance the RE200 from TP Link which cost around 20 euros.
First connect your phone to 3G / 4G / 5G, then share your phone's connection by making a WiFi Hotspot.
Configure your WiFi Extender to connect to your phone, and then connect an ethernet cable between the WiFi Extender and the LAN port of the POE Adaptor.
Insert a SIM card in the router, and connect an ethernet cable between the Router and the LAN port of the POE Adaptor.
If you wish to manage your ORS using panel.rapid.space, you need to make sure your ORS is connected to the internet without firewall in order for re6st to work properly on the ORS. Here are different ways to do so.
Use this method if you are comfortable enough with Linux. Please note depending on your linux distribution the procedure might be different.
For this you need to have a ethernet port on your laptop, or use a USB to ethernet adaptor.
First connect your phone to 3G / 4G / 5G, then share your phone's connection to your laptop using USB tethering or by make a WiFi Hotspot.
Activate IP masquerading on your laptop:
iptables -t nat -A POSTROUTING -o <phone-network-interface> -j MASQUERADE
Then, you need to run a DHCP server on your laptop's ethernet interface. Check if your network manager has such function, otherwise you can disable it for the ethernet interface and use other software such as dnsmasq.