Población indirecta de Textarea en formulario HTML usando PHP

I am working on an "Update User Data" form, which should reflect the initially entered information stored in the database into the textarea, and can be changed if the user wishes to. While I'm doing so, I have a concern - is directly writing value = <?php //some code ?> the safest bet?

I was trying to invoke a function to place my PHP code in that instead, but apparently it's just displaying the function's name.

Aquí está mi fragmento de código:

<div>Date of Birth: </div>
    <input id="dob" type="date" onFocus="emptyElement('status')" value="reflect_data('dob');">

where the function reflect_data is defined as -

function reflect_data(elem) {
//query and some code to access the data and store into $member

if (elem == "dob") {
    echo $member['DOB'];
    exit();
}

NOTE : A newbie to PHP, any advice would be welcome. Thanks. :)