JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="phone">
<button disabled>pew</button>

JavaScript

const checkLength = function(evt) {
  if (phoneField.value.length > 5) {
  	button.removeAttribute('disabled')
  }
}

const phoneField = document.querySelector('input[name="phone"]')
const button = document.querySelector('button')
phoneField.addEventListener('keyup', checkLength)