I would be interested, too, but only to see how they would phrase a response .
You really need to use a genuine Google App requiring genuine Google services on a degoogled phone?
I can think of two solutions:
Solution 1: Correct the flawed premise and get rid of the need to use the App.
If you want to stay with /e/, rethink your use case and make it work without the App.
/e/ has no Google services. It comes with microG to have at least some compatibility with Google-dependent Apps. This works well enough for a lot of such Apps, and not so well for other Apps (including Google Voice, seemingly).
Even if microG at some point in time could mimic Google services good enough to enable Google Voice to work, you couldn’t reliably count on it, as Google could break this at any given moment with changes on their side, with microG having to catch up again, if at all possible. So failures and outages for Google-dependent Apps are an always looming possibility with /e/.
Solution 2: If you really can’t live without the App working reliably, get rid of /e/ and regoogle the degoogled phone.
If you don’t want to return to the stock OS for your device, you could use LineageOS instead of /e/, install the necessary amount of genuine Google services via something like Open GApps on it, and use the device registration for using Google services on a Custom ROM to not endanger your Google account with violating Google TOS.
This can’t be done with /e/, because the genuine Google services can’t be installed alongside microG, which tries to fake the presence of those exact services, so /e/ is the wrong OS for running Google-dependent Apps you really need as long as there’s no version without microG. And it could still be the wrong OS for this even without microG because genuine Google services, once installed, might fail to work reliably because of missing stuff due to the further degoogling of /e/ compared to LineageOS.