To make something be visble or hidden on a specific device, just put the HTML in a [show_if] or [hide_if] shortcode as explained in the Add-Ons page. Like
[hide_if device='phone']your image html[/hide_if]
To change the alignement of your text on mobuile, give it a class and then use custom CSS to style it different on phones.
Like using
<p class=”mytext”>your text</p>
then add the rule below in Main Options > Fonts & Custom > Custom CSS Rule box
.is-phone .mytext {text-align:center;}
mobile classes you can use are
.is-desktop
.is-smalltablet
.is-phone
.is-mobile