there isn't a way to push data from a web server to a web browser using just php & html.
Instead, use a meta tag between the <HEAD> </HEAD> tags like so:
<META HTTP-EQUIV="REFRESH" CONTENT="120; URL=yourpage.php">
this way the web page will refresh every 2 minutes (120 seconds). if someone else has inputted data into the database the manager will now see the new data.
if a popup box is necessary, then consider using a javascript alert() function when new data is available.