Dear HR professional,
We presume you are from a company (not a Recruitment Consultant) and your domain is Non-IT. Even among Non-IT engineers, there is a tendency for no-shows after attending three rounds of interviews, and at the final stage, they become incognito. The telephonic interview is the first level of filtering (very important too) process after the scrutiny of the resume you have about that candidate. As rightly said by another member here, in the first level of interaction over the phone, you need to cross-check the candidate's relevant experience matching the job specifications you have in terms of process, domain, etc. You need to spend quite a good amount of time in this process by asking probing questions and sometimes recapping a question during the process in a different way. This will provide a lot of informative resources about the person and their fitment.
Most of the 2-5 years of experienced candidates may look for a change (which may be their second change mostly) for branded, professional companies with systems and procedures, good policies, and a good hike in pay from the present one to have a reasonably settled career for the next few years to stabilize. All these factors have to be kept in mind when you do the initial selection process through a telephonic interview. If a candidate gets a good score in your first level of the telephonic interview, only those candidates should be called for a personal interview.
As long as we have a dearth of quality people resources, you will need to swim along in the ocean of Recruitment with incognito fishes. Be happy and work your process.