Yes that's entirely possible. Basically all that happens here is the value which is echoed by PHP gets embedded in the JS and the whole JS block is then passed to the browser, which runs it - effectively the same as if you'd hard-coded the value instead of echoing it.

The issue you'll have with this specific code is that you can't echo within an echo...instead just concatenate the value into the string you're already building!

e.g.

<?php echo "<script> javscript_function(".$php_number_variable."); </script>"; ?>

Or, since you're using double-quote strings, the variable can be interpolated directly:

<?php echo "<script> javscript_function($php_number_variable); </script>"; ?>