I need the Billing Address Phone Number to be mandatory for payment provider purposes

[ben_varoom]

How can I set the Billing Address Phone Number to be mandatory in Checkout?

I have Shipping Address Phone Number as Mandatory, but see no way of ensuring that the Billing Address Phone Number field is Mandatory. This is required for my payment provider. Many people must have come across a similar issue, please advise. 

Many thanks.

[ThibCar]

Same issue here. I am hoping Shopify could allow us to make the billing phone number a mandatory field.