[ElfMage]

Take a look at the lookaround syntax described here: http://www.regular-expressions.info/refadv.html

You could use something like this:

'[\d]{7,11}(?![\d]+)'

This uses a zero-length look ahead.

The problem with the look-behind is that some regex engines only allow plain text in the look-behind.

But, if you know what could be before the number you are matching, you could craft that into the regex.

I am sure there is a simpler way....