Multiple Columns

You can use Ordered Lists to display multiple fields on a single line

HTML:

<ol class="singleline">
<li> <label for="cf7-phone">Phone: </label> [text cf7-phone id:cf7-phone]</li>
<li> <label for="cf7-mobile">Mobile: </label> [text cf7-mobile id:cf7-mobile]</li>
</ol>

Added to Form section of CF7 interface. Labels are added for improved accessibility.

CSS:

.wpcf7-form ol.singleline {
list-style: none;
margin: 0;
}

.wpcf7-form ol.singleline li{
display: inline-block;
float: left;
margin-right: 10px;
padding-right: 10px;
}

Add via Child Theme or use custom CSS plugin.

Or, you could also use the add-on CF7 Skins Ready to make a 2 column contact form.