This has also been reported by other users and has also been verified by the folks at ArsTechnica. Note that Facebook doesn’t actually know the contents of your phone calls or text messages, but rather the information is more along the lines of who you’ve contacted and when you have contacted, as reported by McKay who shared a log which showed the different times he contacted his partner’s mom.
Downloaded my facebook data as a ZIP file
Somehow it has my entire call history with my partner's mum pic.twitter.com/CIRUguf4vD
— Dylan McKay (@dylanmckaynz) March 21, 2018
While this sounds alarming, it seems that this is something that users might have unknowingly granted Facebook access to. In a statement made to ArsTechnica, a Facebook spokesperson said, “The most important part of apps and services that help you make connections is to make it easy to find the people you want to connect with. So, the first time you sign in on your phone to a messaging or social app, it’s a widely used practice to begin by uploading your phone contacts.”
This seems to only affect Android devices because iOS has never allowed silent access to call data. That being said, the good news is that if you’d rather not give Facebook access to said information, there is a way to delete your uploaded contacts from Facebook.