The issue here is that Android has failed to exclude emergency calls from being routed to a VoIP provider. If it wasn't MS Teams causing this issue it could well have been another registered VoIP provider on that phone.
It's simple. Force it to go through the regular cellular network first, and if it doesn't exist (e.g. because you're on a WiFi-only tablet) or is unreachable then try to fall back to another app.
