To give you the inverse perspective, an OG blogger named Steve Yegge made a list of five essential phone screen questions:

https://sites.google.com/site/steveyegge2/five-essential-pho...

Question three is this:

Last year my team had to remove all the phone numbers from 50,000 Amazon web page templates, since many of the numbers were no longer in service, and we also wanted to route all customer contacts through a single page.

Let's say you're on my team, and we have to identify the pages having probable U.S. phone numbers in them. To simplify the problem slightly, assume we have 50,000 HTML files in a Unix directory tree, under a directory called "/website". We have 2 days to get a list of file paths to the editorial staff. You need to give me a list of the .html files in this directory tree that appear to contain phone numbers in the following two formats: (xxx) xxx-xxxx and xxx-xxx-xxxx.

How would you solve this problem? Keep in mind our team is on a short (2-day) timeline.

In Yegge's case, he explicitly does NOT want a hand-written program, he wants the candidate to suggest a CLI tool, e.g.

grep -l -R --perl-regexp "\b(\(\d{3}\)\s|\d{3}-)\d{3}-\d{4}\b" > output.txt

———

So...

These questions aren't good or bad unto themselves, but when the person asking is engaging in "Guess the answer I'm thinking of," don't beat yourself up if you guessed wrong. Your answer might be prized by someone else with an enormous amount of experience hiring engineers.