Sorry for the late reply, it's very dark where the ONT is hiding, I have it wall mounted behind the sofa so nobody can see it.
But as you can see, there are two PSTN ports, TEL1 is for your main landline number that will be assigned, and I believe the guy who installed it says the ONT hardware itself supports having two numbers on the same line, but PTCL doesn't offer that, so the second port goes unused.
This is an Alcatel Lucent ONT, the ones they're installing now are either FiberHome or ZTE, so they may not look exactly like this, but you get the point.