Unfortunately Echo in VOIP calls is already closed.
According to https://bugtracker.fairphone.com/project/fp2-android9/issue/25 the problem - callers hear their own echo in VoIP calls (messengers, SIP-apps, …) - should be fixed since Android 9 (beta 20.06.2-beta.0) in June.
Can anybody confirm that this problem does not exist any more?
Does anybody have an idea, wether this will be included in other operating systems (eg. Lineage OS 17)?