PHP allows you to call function by value and reference both. In case of PHP call by value, actual value is not modified if it is modified inside the function.
Let's understand the concept of call by value by the help of examples.
In this example, variable $str is passed to the adder function where it is concatenated with 'Call By Value' string. But, printing $str variable results 'Hello' only. It is because changes are done in the local variable $str2 only. It doesn't reflect to $str variable.
Let's understand PHP call by value concept through another example.