we need scripts that collect the information's from our web visitors and send it to google sheets

hello
I have a web page with an HTML form that collects the visitor's information into my database using an external PHP script (check the attached file inside my-host.zip) that comper the phone number if it already exists in the database or not
if yes the script tells the visitors to add a new number because someone is already registered with the same phone number
if no the script takes the leads and adds a date to every visitor then put them into my database
I hope this was clear

Now I want to make this process like this:

-step 1 (check the image)
-step 2 check if the data (phone number) previously exist in the database or not, if yes I need to notify the visitor (someone is already registered with the same phone try another one), I prefer if this step appears in the same tab
-step 3 (check the image)

any other questions or ideas about these 3 steps tell me.

thanks!
Tarek.