There are things mixed up here, and it's my fault for bringing two different things in the mix.
In the case of the advice given to OP to give their phone number because recruiters won't use their contact email, it's situational.
If the resume is good enough and the position not easy to fill, the recruiter will use the email, because it would be unprofessional in these conditions to pass on a good applicant just because of lazyness.
If you work for a company where good applicants are legion and you can be that picky, well, considering the competition in the space, lucky you ^^'
Now, for the prospection case, I don't think the reason for trying to go for the phone call is data collection. Point is, emails get people to think. A developer considering changing jobs will read them, but only reply if the content is tempting enough: company clearly stated, guarantees that everything will be great (recruiting process, salary, advantages, work environment...)
However let's face it, most jobs are average / low bar, and developers knowing their worth won't even consider them. So recruiters who aren't lucky enough to have dream jobs amongst there clients have two options:
- refusing to work for companies with low standards, and specialize in giving only good positions. This is a risky long game, requires investment in assessing the companies, then building trust and reputation.
- forget about it, and play the numbers game. This is the setting where phone calls are more "efficient": it's all commercial techniques, don't give away much, favor direct contact to force people to agree to things they wouldn't if they had all the data and thinking time. This produces more matchings, so more money for the recruiter. Downside: it allows companies with crappy practices to still get a share of the applicants' pool, especially if they can afford a big turnover anyway.
Note: of course you can consider that playing the numbers is what gives you food, so, too bad for the developers who wasted time in crappy recruitment processes or even crappy jobs because of that. And I'm not saying all the pairings are for crappy jobs anyway, you can also have average or underestimated ones that just don't stand out in the market.
My point here is mostly that no, using email isn't a stupid way to get the job done, it's efficient if what you have to offer is demonstrably good. If your job offers are unattractive though, that's when you need to use phone calls and persuasive techniques.
And that's the reason I refuse discussions made through phone or in person contact right at the beginning: it doesn't let me fact check and explore options, and I may be pushed to agree to a pointless interview just because of a good "salesman recruiter". It's a waste of time.