When using API, add Client's contact info to form for submitting job openings

When using API, add Client's contact info to form for submitting job openings

I am using the API to allow client's to add new job openings directly from our website. 

However, I don't see how to use the API to also allow them add their contact information via that form. If they can't add their contact information, then how will we get in touch with them once they have submitted a job?

I know that there are different modules, and that I am using the Job Openings module for this particular form - but the information I need to use WITH this form is in the Client Contacts module I think.

I'm using the form on a WordPress site - I've attached the code for the form, and for the functions file. It would really be helpful if someone could help me specifically add to what I have already so that I end up with the client's email, address and phone number in my form, then I could be done with this part of my project.