How can i validate integer form in php?

I want to validate integer form using PHP. Do anyone of you know how to validate it?
my code like this
`
Thông tin thành viên
">

        First name : 

        Last name : 
        User Name: 
        Password: 
        Email: 
        Phone: 
        Cấp độ : 
                            
                
                    ---Free choose---
                    Administrator

                    Member
                
            
        
        
         
    `

When people input the phone i want to check whether it is integer or not? can you help?

Answer

Try using this is you want to check it on runtime.

Phone: 

Or use is_int or is_numeric if you want to check the phone number after POST.