BVR boardview for an iPhone 8 Plus, with the name indicating the Intel baseband version of the logic board; the file is 379 KB. No board number or revision is given beyond that. Intel and Qualcomm modem boards differ in layout around the baseband section, so make sure your phone carries the Intel variant before relying on it. Technicians use this map to find components, trace nets between the sandwiched board layers and pick test points for diode-mode and voltage checks when hunting shorts or no-power faults.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @GENERAL_SMART_PHONE_SCHEMATICS. Enginerys does not host this file.
How to open a .bvr file
Text boardview from the BoardView R family of tools, seen for Lenovo, MSI and Clevo boards.