Only show list option based on earlier form choice - php

Question

Here's part of my form:
<label for="User">Select your account type:</label>
<select name="usertype" for="usertype" id="usertype" required>
<option value="1">Employee</option>
<option value="2">Manager</option>
</select>
<label for="User">Select the company you work for:</label>
<select name="company" for="company" id="company" required>
<?php
include ('processors/generate-company-list.php');
?>
<option value="NULL">I'll create my own company later</option>";
</select>
I only want <option value="NULL">I'll create my own company later</option> to be available if they choose to be a manager earlier in the form. Is this possible?

Answer 1

<script type="text/javascript">
function check(){
var usertype=document.getElementById("usertype").value;
if(usertype==2){
document.getElementById("company").selectedIndex = "0";
document.getElementById("company").disabled=true;
}else{
document.getElementById("company").disabled=false;
}
}
</script>
<label for="User">Select your account type:</label>
<select name="usertype" for="usertype" id="usertype" required onchange='check();'>
<option value="1">Employee</option>
<option value="2">Manager</option>
</select>
<label for="User">Select the company you work for:</label>
<select name="company" for="company" id="company" required>
<?php
include ('processors/generate-company-list.php');
?>
<option value="NULL">I'll create my own company later</option>";
<option value="1"> listitem1 </option>";
<option value="1"> listitem2</option>";
</select>
I used javascript function to select 0 index whenever manager is selected and disabled second select box.