Lightweight PHP / Ajax / Validation Form with NO JQUERY

I need an extremely fast loading and secure form in php with validation. Please do not use a large library like jQuery. This form needs to send an email with the 4 fields below, the user's IP address, and user agent. Here is the form: <form> <div class="field"><input type="text" name="name" placeholder="First and Last Name"></div> <div class="field"><input type="text" name="email" placeholder="E-mail Address"></div> <div class="field"><input type="text" name="phone" placeholder="Phone Number"></div> <div class="field"><textarea rows="4" name="details" placeholder="Additional Details"></textarea></div> <div class="field"><input type="submit" value="Submit"></div> </form>