PHP: strtotime() - consistent results

How venerable is this to the settings of the server?

echo date('F j, Y',strtotime('2015-2-7'));

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In some locations, 2015-2-7 could be considered February 7, while in other places it could be considered to be July 2.  What is the most foolproof way to create a timestamp from  a day, month and year?