如果手机输入错误，我如何验证和提醒？

Question

电话号码和电子邮件必须有效。

这是一个没有电话号码验证的基本弹出式联系表单。我想验证电话号码。我听说过正则表达式，但我不确定如何在代码中实现。

因为我不理解javascrip，但我希望你能帮助我。

<form action="#" method="post" id="form">

    <h2>Contact Us</h2><hr/>
    <input type="text" name="company" id="company" placeholder="Company"/>

    <input type="text" name="name" id="name" placeholder="Name"/>

    <input type="text" name="email" id="email" placeholder="Email"/>

    <input type="text" name="phone" id="email" placeholder="Phone"/>

    <a id="submit" href="javascript: check_empty()">Send</a>

</form>


function check_empty(){
    if(document.getElementById('company').value == "" 
    || document.getElementById('name').value == ""
    ||document.getElementById('email').value == ""
    ||document.getElementById('phone').value == "" ){
    alert ("Please, fill the fields!");
    }
    else {  
        document.getElementById('form').submit();
    }
}

//function to display Popup
function div_show(){ 
    document.getElementById('abc').style.display = "block";
}

//function to check target element
function check(e){ 
    var target = (e && e.target) || (event && event.srcElement); 

    var obj = document.getElementById('abc'); 
    var obj2 = document.getElementById('popup'); 

    checkParent(target)?obj.style.display='none':null; 
    target==obj2?obj.style.display='block':null; 

} 

//function to check parent node and return result accordingly
function checkParent(t){ 
    while(t.parentNode){ 
        if(t==document.getElementById('abc'))
            { 
                return false 
            }
        else if(t==document.getElementById('close'))
            {
                return true
            } 
        t=t.parentNode 
    } 
    return true 
}