In macOS 10.14 or newer, PhoneView needs special permission to access the iTunes backup folder. To give PhoneView access:
Open the Security & Privacy panel in System Preferences.
Pick the Privacy tab.
Click the padlock icon to make changes, and enter your Mac's admin password when prompted.
Pick the Full Disk Access section. (You may need to scroll down in the list in the left-hand sidebar.)
Drag the PhoneView app from your Applications folder into the list of allowed apps.