It is real simple. LibrePhotos does not phone home. However, if Libre Photos ever decides to collect any information it will be opt-in. You will have to explicitly say yes it is ok.
You may be asking why would Libre Photos ever need to send back information. To put it simply it would be for error reporting, allowing the development team to id and fix issues more swiftly. Once again this would be opt-in, and we would tell you exactly what is being collected.