How to make call on other iPhone

Almost the exact same question has been asked before, but no answer was forthcoming. So I'm trying again in the hope someone can help.

I have 2 iPhones, one with a SIM and which I can use as a regular cellphone and the other has NO SIM which means it is restricted to data based communication, like Messages, FaceTime etc.

Enabling 'calls to other devices' on the iPhone with SIM means incoming cellular calls can be taken on either iPhone - just as it is supposed to work. However, how can the reverse be done, i.e. make a call from the iPhone WITHOUT SIM, via the iPhone WITH SIM?

This technique can be used with other devices, like iPad and/or Mac, from which calls can be made via the iPhone WITH SIM, but I cannot see a way to do this from one iPhone via the other.

If the Phone app is used, the call simply fails so it is trying to use a non existent SIM and unsurprisingly failing. If I try to use FaceTime, it just sees the number as not being a 'FaceTime number' as asks to send an SMS invitation.

Which means neither method is taking into account that another iPhone is available that can be used to make calls to regular numbers. So either I'm missing something here and there's some other way to do it, or this is not something Apple have allowed for and hence is currently impossible.

Please note, I am not looking for alternative ways to make calls. I am specifically trying to do what I have described above and make a call to a regular number, from an iPhone WITHOUT SIM, via an iPhone WITH SIM. A process that works as it should in reverse, but has anyone managed to MAKE calls this way?