This kind of situation is mostly due to the VCF file lacking necessary tags or not being in the right format. There are a lot of online CSV to VCF converter tools that produce VCF files that are technically VCF but do not comply with the structured format of Android. When a device doesnt find the contact fields, it goes on to ignore the file without any notification. Character encoding in several characters can also be an issue, particularly if your CSV has special characters or Unicode names. A trustworthy CSV to VCF Converter will guarantee the correct vCard version (2.1 or 3.0), the right mapping of fields, and the clean encoding so that your phone will be able to import everything without any trouble. Just before to the import have a look at the VCF file through the lens of a text editor and verify if the BEGIN:VCARD and END:VCARD tags are proper. The use of a professional tool fixes these issues in more than 90% of cases.