JSFiddle - React, Tailwind, and code Playground

HTML

<label class="labelinput" for="phonenum">Phone Number:</label>
<input type="text" id="cell" name="cell" class="forminput" />
<button>check</button>

JavaScript

$('button').on('click', function () {
    if (!/^[0]\d{9}$/.test($('#cell').val())) {
        alert('wrong phone number');
    }
});