JSFiddle - React, Tailwind, and code Playground

HTML

<select id="contactSelect" style="width: 100px; text-align: center;">
  <option value="email">Email</option>
  <option value="telephone">Phone</option>
</select>
<p id="contact_method">Please supply your Email Address</p>
<input type="text"/>

JavaScript

document.getElementById("contactSelect").onchange = function() {
    var value = this.options[this.selectedIndex].value;
    if(value == 'telephone') {
        document.getElementById("contact_method").innerHTML = 'Please supply your phone number';
    } else {
        document.getElementById("contact_method").innerHTML = 'Please supply your email address';
    }
}