JSFiddle - React, Tailwind, and code Playground

HTML

<strong>Gratis Rådgivning</strong><br/>
<span>Før, under, efter parforholdet<br />
Ring <span style="color: #ffffff;"><span style="font-weight:bold"><a href="tel:70116263"><span style="color:#000"><br class="br-on-mobile">
  <strong>70 11 62 63</strong></a>
</span></span>

CSS

.br-on-mobile {
  display: none;
}

@media screen and (max-width:400px) {
  .br-on-mobile {
    display: inherit;
    padding-left:20px;
  }
  
}