Adding new contact button

Hi there,

I need to create one more contact button at the job page https://prntscr.com/ghvmag
This button is needed to display the phone number of the employer.

As I understand, I need to create one more field “Phone number” at the job submit page. Than somehow output this filed into the button.

What code should I edit to create a new button, which will allow candidates see the phone number without a registration?