<div class="form-group">
  <input type="tel" class="form-control input-lg" id="mobile" name="mobile" placeholder="请输入手机号码">
</div>
<div class="form-group">
  <div class="input-group">
    <input type="tel" class="form-control input-lg verify-input" id="verify" name="verify" placeholder="请输入验证码" >
    <div class="input-group-btn">
      <span class="input-group-btn">
        <input value="获取" class="btn btn-info btn-lg verify-btn" id="get_verify" type="button">
      </span>
    </div>
  </div>
</div>

$('#mobile').on('input',function(){
  var mobile = $(this).val();
  if(mobile.length == 11) {
    $('#get_verify').focus();
    return false;
  }
});