: If this is a corporate "Telephone Book" for a company using Remote File Sharing (RFS) , it might be distributed through a private MDM (Mobile Device Management) platform rather than a public link.
: In Germany, "Telefonbuch" apps are commonly provided by major telecommunications companies. You can find official versions of standard directories on the App Store by searching for "Das Telefonbuch." download-rfs-telefonbuch-ipa
If this is a specific internal company app, you should contact your for the secure, official download link. : If this is a corporate "Telephone Book"
An (.ipa) is the archive format used by Apple for iOS applications. Downloading these from unofficial sources is generally not recommended due to security risks. Abbreviations in Data Communications | PDF - Scribd
Could you clarify if this app is for a or associated with a particular software suite ? Abbreviations in Data Communications | PDF - Scribd