I\'ve not used PHP much (or at all) before, and I have the following code:
iFrames just take a url - and parameters can be embedded in urls just fine.
The problem, if I understand the question clearly, is that you're mixing up your quotes:
echo "";
will be outputted as
where 21254545 is an attribute of the iframe instead of part of the url.
Assuming that you don't actually need the quotes in the url, change the echo line to:
echo "";
And it should work.