Responsive text and image

As a complement to Hugo's response, Bootstrap already has tools to change the display property by varying it according to the width of the viewport (through media queries ). They are the d-* ( documentation classes).

OBS : When referring to xs , this is screen size (

Already in the image you would use:

<img class="d-inline-block d-sm-none" src="...">

xs causes d-inline-block to be img , and display: inline-block causes it to be d-sm-none for display: none or larger screens, ie it will only be visible on% / p>

In this way the visibility of sm and xs are mutually exclusive.

Example:

html, body {
  padding-top: 40px;
}

<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css">

<main class="container">
  <div class="row">
  
    <button class="btn btn-lg btn-info btn-block text-uppercase">
      <span class="d-none d-sm-block">Prosseguir</span>
      
      <img class="d-inline-block d-sm-none" src="https://getbootstrap.com.br/docs/4.1/assets/brand/bootstrap-solid.svg"style="max-width: 50px;">
      
    </button>
    
  </div>
</main>

You can leave the snippet in full screen (full page link) and change the width of your browser window to see responsiveness working     

There are several ways to do it and one of them is putting span inside button as I did in this example. then with the @media rule you hide and show this span , at the same time that you remove the text from bottun by putting font-size:0 for example.

Then if the screen has a maximum width of% width, the image appears, if it is more than 610px the text of 610px appears. You can adjust this in the rule button if you want

Atfirstyoumaythinkitisnotafullysemanticform,buttheupsideisthatevenwith@mediathetextmaystillbevisibletoscreenreaders,butitdoesnotappeartotheregularuser.

Seethecodefortheimageabove:

.icon {
    height: 16px;
    width: 16px;
    background-image: url(https://placecage.com/16/16);
    vertical-align: middle;
    display: none;
}
@media screen and (max-width:610px) {
    .icon {
        display: inline-block;
    }
    button {
        font-size: 0;
    }
}

<button class="btn btn-lg btn-info btn-block text-uppercase" id="prosseguir" type="submit">
    Prosseguir
    <span class="icon"></span>
</button>