To include the CSS and JavaScript files in the HTML file, append the following to `signup.html`:

```html
<!DOCTYPE html>
<html>
    <head>
        <title>Signup</title>
        <link rel="stylesheet" type="text/css" href="signup.css">
    </head>
    <body>
        <form id="signup-form">

                ...

        </form>
        <script src="signup.js"></script>
    </body>
</html>
```

`signup.js` needs to be updated to post the form data to the server:

```javascript
const form = document.querySelector("#signup-form");
const passwordInput = document.querySelector("#password");
const passwordConfirmInput = document.querySelector("#password-confirm");

form.addEventListener("submit", (event) => {
    event.preventDefault();

    if (passwordInput.value !== passwordConfirmInput.value) {
        alert("Password and password confirmation do not match.");
        return;
    }

    const firstName = document.querySelector("#first-name").value;
    const lastName = document.querySelector("#last-name").value;
    const email = document.querySelector("#email").value;
    const phone = document.querySelector("#phone").value;
    const password = passwordInput.value;

    let data = {
        firstName,
        lastName,
        email,
        phone,
        password
    }

    fetch('signup', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json'
        },
        body: JSON.stringify(data)
    })
        .then(res => res.json())
        .then(res => {
            if (res.success) {
                // TODO: Handle success case, for example redirecting to the home page
            } else {
                // TODO: Handle error case, let the user know given input is invalid
            }
            console.log(res.message);
        })
        .catch(err => {
            // TODO: Handle error case, let the user know something went wrong
            console.log(err);
        });
});
```

Note that in `signup.css` I have incorrectly added a line containing "CSS:". That line should be removed. Apologies for that.


To deploy, one option is to use Node.js with express. Create a file `server.js`:

```javascript
const express = require('express');
const app = express();

const host = 'localhost';
const port = 8080;

// Enable parsing of incoming requests with JSON payloads
app.use(express.json());
// Serve static files such as CSS, JS, images, ...
// Note: usually static resources are served in a '/public' folder
app.use(express.static(__dirname));

// Signup route
app.get('/signup', (req, res) => {
    res.sendFile(__dirname + '/signup.html');
});
app.post('/signup', (req, res) => {
    if (validateSignupBody(req.body)) {
        // TODO: handle signup data, such as writing it to a database.
        // NOTE: Encrypt password before writing to the DB!
        res.send({ success: true, message: 'Signup complete!' });
    } else {
        res.send({ success: false, message: 'Signup failed!' });
    }
});
const validateSignupBody = (body) => {
    // TODO: validate correctness of received data
    return true;
}

app.listen(port, (err) => {
    if (err) {
        console.log("error while starting server");
    } else {
        console.log(`Server is running on http://${host}:${port}`);
    }
});
```

Install express using `npm install express`.
Finally, run the server: `node server.js`.

Now you're ready to test your signup page by going to `http://localhost:8080/signup`.


Note that these are simple example scripts which are lacking functionality and structure. In a real world application the code and project structure would be different to ensure maintainability of the code.
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