Masked phone input

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>Request a call</title>
    <style>
      *, *::before, *::after { box-sizing: border-box; }
      body {
        margin: 0;
        padding: 32px 16px;
        font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
        background: #f4f4f5;
        color: #18181b;
      }
      .card {
        max-width: 460px;
        margin: 0 auto;
        padding: 28px;
        background: #fff;
        border: 1px solid #e4e4e7;
        border-radius: 12px;
      }
      h1 { margin: 0 0 6px; font-size: 20px; }
      .sub { margin: 0 0 22px; font-size: 14px; color: #71717a; }
      .field { margin-bottom: 16px; }
      label { display: block; margin-bottom: 6px; font-size: 13px; font-weight: 500; }
      input, textarea, select {
        width: 100%;
        padding: 10px 12px;
        font: inherit;
        font-size: 14px;
        color: #18181b;
        background: #fff;
        border: 1px solid #d4d4d8;
        border-radius: 8px;
      }
      input:focus, textarea:focus, select:focus {
        outline: 2px solid #18181b;
        outline-offset: 1px;
        border-color: transparent;
      }
      textarea { min-height: 110px; resize: vertical; }
      button {
        width: 100%;
        padding: 11px 16px;
        font: inherit;
        font-size: 14px;
        font-weight: 500;
        color: #fff;
        background: #18181b;
        border: 0;
        border-radius: 8px;
        cursor: pointer;
      }
      button:hover { background: #3f3f46; }
      button:active { transform: scale(0.99); }
      button[disabled] { opacity: 0.6; cursor: default; }
      /* Hidden from people, filled in by bots. Never remove it. */
      .hp { display: none; }
      .hint { margin: 6px 0 0; font-size: 12px; color: #a1a1aa; }
    </style>
  </head>
  <body>
    <form class="card" action="https://app.portform.co/api/submit" method="POST">
      <h1>Request a call</h1>
      <p class="sub">Leave a number and we'll ring you back.</p>

      <input type="hidden" name="access_key" value="YOUR_ACCESS_KEY" />
      <input type="checkbox" name="botcheck" class="hp" tabindex="-1" autocomplete="off" />

      <div class="field">
        <label for="name">Name</label>
        <input id="name" type="text" name="name" autocomplete="name" required />
      </div>
      <div class="field">
        <label for="phone">Phone</label>
        <input id="phone" type="tel" inputmode="tel" autocomplete="tel" placeholder="+1 (234) 567-8900" required />
        <!-- What actually gets sent: digits only, no formatting to undo later. -->
        <input type="hidden" name="phone" id="phone_raw" />
        <p class="hint">US format. We only call, we never text.</p>
      </div>
      <div class="field">
        <label for="message">Anything we should know?</label>
        <textarea id="message" name="message"></textarea>
      </div>

      <button type="submit">Request a call</button>
    </form>

    <script>
      const input = document.getElementById('phone')
      const raw = document.getElementById('phone_raw')

      input.addEventListener('input', () => {
        const digits = input.value.replace(/\D/g, '').slice(0, 11)
        const national = digits.length === 11 && digits[0] === '1' ? digits.slice(1) : digits
        const [, a, b, c] = national.match(/^(\d{0,3})(\d{0,3})(\d{0,4})$/) || []

        input.value = [a && `(${a}`, a.length === 3 ? ') ' : '', b, c && `-${c}`]
          .filter(Boolean)
          .join('')
        raw.value = digits ? `+1${national}` : ''
      })
    </script>
  </body>
</html>