I suppose you could do this, by having PHP first read the 'content' page file itself, scanning for the text between the <title> tags and then "echo"ing the resulting text as the title for the frameset.
Something like:
$f = fopen ("content.html","r");
... loop round the file, scanning the html for the <title> and store it in $title ...
fclose ($f);
echo "<title>$title</title>";
How successful this is rather depends how consistent you've been in setting up the content page <title> tags.