Syncing
Mac Book Pro won't sync with iPhone after installing Seagate backup software.
MacBook Pro 13", macOS 10.13
Mac Book Pro won't sync with iPhone after installing Seagate backup software.
MacBook Pro 13", macOS 10.13
... and if you are syncing via iTunes, as kaz-k suggests, are you doing so via USB or Wi-Fi? Also, is your iTunes Library/Media folder on your Mac or this external Seagate drive?
How were you syncing between your MacBook Pro and your iPhone before? ... iCloud?
Syncing