Thanks Shiach, good to know.
It turns out my issue was a false alarm. The outgoing audio from the L5 was cancelled out by the receiving phone as I was doing the test myself with the two phones close to each other. Once I tested them distanced (in separate rooms), I could hear the L5 audio just fine 
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Thank you for running this down. Just got my L5 the other week and this is one of the problems I encountered. The workaround suggested by the GNOME team is laughable. It’s also frustrating to learn the issue for this bug was opened on April 26th 2021 and there appears to be no progress made on implementing the feature.
These are the kinds of things that cause users (and buyers!) to throw up their hands and give up on products like the Librem 5. If there’s anyway for Puri.sm to coordinate with the GNOME team or submit their own pull request to get this working in GNOME calls that would be a big win imo. If it’s worthwhile to open a support request with Purism to track this, I’ll do that as well.