php convert datetime to UTC

Question

I am in need of an easy way to convert a date time stamp to UTC (from whatever timezone the server is in) HOPEFULLY without using any libraries.

Answer 1

As an improvement on Phill Pafford's answer (I did not understand his 'Y-d-mTG:i:sz' and he suggested to revert timezone). So I propose this (I complicated by changing the HMTL format in plain/text...):