A “catch phrase” can be as simple as adding the sentence “Please mention ‘yellow dragon’ in your application” to your job description - which can be used to wield out the applicants who didn’t really read your job offering, but just decided to spam you with a cover letter template. In most cases, you don’t want to employ this kind of contractors.
I kept this job open for 9 days (which is indeed a long time - otherwise the number of withdrawals would have been a lot smaller). Either way, this method allowed me to narrow my search down to less than 1/5th of the applications in a short timeframe. If you can spend that time, or just start using catch phrases, you can avoid spending some time during the hiring process, especially for smaller jobs.