How to setup pihole with an ONT style router setup?

I shifted homes and my new place comes with a connection that is ONT.

The router unit is a Phyhome P20 ONT. I don't have the option to assign static IP to devices, nor set another device as a DHCP server.

Is it possible to run a pihole effectively in such a setup? I honestly wanted to install OpenWRT, but I understand that it isn't possible with ONT style setups.