The Eagles are 2-6 with backup QBs starting since Nick Foles left after the 2018 season. 

They were 10-3 with Nick Foles starting as the backup QB in 2017-2018 (including playoffs).

In 2014 and 2015, they were 4-6 with a backup QB.

In 2012-2013 with Foles technically as backup both years, they were 9-8 in Foles' starts.