Ajax Field + API Integration

I have a .html page which asks the user for their name and email and this data is sent to a third party email provider when they hit submit. I need a ajax field added so that after they put in their email onfocus a phone number fields slides down below and asks them to put in their phone number. if they put in a phone number this phone number should be sent to a simple api i provide + subscribe the user to the mailing list. if they don't provide a phone number still subscribe them. should be very easy. One thing should be noted that the we use use two different providers for the email collection and the phone number collection. we use icontact for the email and redfish for the phone number. We already have icontact working. i attached the redfish api. we need the first one which is Subscribe