Spreadsheet contact sheets like XLSX are designed for tabular data, not for live contact syncing. Mobile devices expect a structured contact file where each entry follows a defined contact file standard. Excel contact columns often store phone numbers, country codes, and labels as plain text, which leads to unsupported contact formats during mobile contact import. This is why spreadsheet contact data may work on one system but fail on Android or iPhone. Digital contact formats like VCF use predefined attributes for names, numbers, and addresses, making them device-friendly. Converting spreadsheet contacts into a structured format using a reliable Excel to vCard converter helps normalize data and avoids sync failures. For users managing contacts offline , tools like Softaken Excel to VCF Converter are often preferred because they preserve contact fields accurately and work without internet access.