The flip side of trying to "solve" that problem is that you then penalise everyone searching for part numbers, which often do look very similar to phone numbers. I suspect they are making an effort to, because I've been bitten by the CAPTCHA-hellban when searching for part numbers. (Likewise, the results there are also often clogged by a bunch of useless sites claiming they have the datasheet or are selling the part, when all they do is try to show ads.)