<a href="#" class="btn btn-secondary bwi-btn" role="button"><span class="bwi-btn-label"><i class="fa-brands fa-whatsapp"></i></span>+31 99 123456</a>

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.2/css/all.min.css">

.bwi-btn {
  position: relative;
  width: 160px;
  text-align: center; 
  padding: 11px 10px 4px 10px;
  outline-offset: 2px;
  border-radius: 6px;
  color: #ffffff !important;
  
  border: 1px solid #ffffff;
  outline: 1px solid #6c757d; 
}

.bwi-btn-label {
  position: absolute;
  display: inline-block;
  width: 30px;
  height: 30px;
  font-size: 15px;
  text-align: center;
  top: -20px;
  left: 64px;
  padding: 2px 0 0 0;
  background: inherit;
  outline-offset: 0;
  border-radius: 100%;
  
  border: 2px solid #ffffff;
  outline: 1px solid #6c757d;
}