In a very limited way, you kind of expect this
(your friend giving your number to someone who they
think you'll get along with, or whatever).
Also, it's worth noting that there is a big difference between "your friend giving your number to someone who they think you'll get along with" and your friend sharing your name and number to some company - for GDPR, the first is covered by the "personal activity" clause 2.2(d), and the latter is not, so GDPR applies and the consent of that friend isn't sufficient, i.e. the friend is permitted to click "share", however, that does not necessarily mean that the company is permitted to use the data shared in this manner. So every company that expects EU users to share their phone contact lists had better be very careful on what and how they do it - you can't rely on informing users or getting consent as you're informing someone else and getting someone else's consent.
This goes a bit sideways on Facebook in two main ways, I think:
1. People are way too fast and loose with who they keep as "friends" on Facebook
2. Facebook has way too much data to warrant a blanket "Yeah, please share -all- of that at once" agreement. Something more granular, like "The phone numbers of your friends who have themselves granted permissions for their friends to share their numbers" would be more reasonable.