buzztone on "[Plugin: Contact Form 7] Responsive contact form"

The actual look of CF7 forms on your website will depend largely on the current WordPress theme used and the CSS styling that theme applies to standard HTML form elements.

To make your form responsive you need to provide responsive CSS styling to the relevant standard HTML form elements, if your theme doesn't do this (the good ones do).

For basic responsive resizing you can start with something like:

.wpcf7-form {
       width: 100%;
}

.wpcf7-form input,
.wpcf7-form input[type="text"],
.wpcf7-form input[type="email"],
.wpcf7-form input[type="tel"],
.wpcf7-form textarea, {
    width: 100%;
}

See Styling Contact Form for a general explanation of styling CF7 forms using CSS.

There is a link at the bottom of the page to a comprehensive and detailed article on Styling Contact Form 7 Forms. The article shows people, with suitable HTML & CSS skills, how to change the appearance of their Contact Form 7 Forms to meet their particular requirements.