PHP code to remove everything but numbers

Try this:

preg_replace('/[^0-9]/', '', '604-619-5135');

preg_replace uses PCREs which generally start and end with a /.

This is for future developers, you can also try this. Simple too

echo preg_replace('/\D/', '', '604-619-5135');

You would need to enclose the pattern in a delimiter - typically a slash (/) is used. Try this:

echo preg_replace("/[^0-9]/","",'604-619-5135');