<fieldset>
<h2 class="fs-title">Enter Your Number</h2>
<h3 class="fs-subtitle">This is step 1</h3>
<input type="text" name="email" placeholder="Phone number" id="PhoneField" />
<input type="button" name="next" class="next action-button" value="Next" id="SendPhone" />

$(document).ready(function() {
        var phoneField = $("#PhoneField").val();
        $("#SendPhone").click(function () {
            alert(phoneField);
        })
    })