PersonPhoneSummaryScreen - Making a field mandatory

Hi,

I'm looking to make the below field mandatory, however it seems impossible to locate frontend and I can't find the place in the DB to make it a mandatory field.

I've found that the field is on the PersonPhoneSummaryScreen. I found the name of the screen via Administration > Customisation > Person > Blocks > personsummaryblock.

There is no Phone entity under secondary entities, yet there is email and address. So I can't edit the field security and make it mandatory as I can with nearly every other field.

Has anyone else been able to make it mandatory? Please advise.

Thanks