It's baffling to me that any popular app wouldn't have 2FA (or any app, for that matter.)
All keylogged/phished/etc.
No more that the password already does. 2FA isn't supposed to protect you from the company you already have the data too. And it's not really for the "privacy" of that personal data but for securing it.
Otherwise, what you're doing is perfectly fine and well enough: connect to your SIP trunk via credentials using a local client and you've more or less got a working, accessible phone number. Unless you truly have a need for Asterisk features, don't bother.
I happen to know first hand of a "voice company" that has a pretty sizeable footprint in the travel/hospitality industry making several million dollars a year and one of their products amounts to nothing more than configuring IVRs and charging through the nose to host them using what is (in my opinion alone) a thoroughly overly-complicated Asterisk infrastructure and similarly overly-complicated dial plans.
"Ring does not alert users of attempted log-in from an unknown IP address, or tell users how many others are logged into an account at one time. Because of this, there is no obvious way to know whether any bad actors have logged into people’s compromised Ring accounts without their consent."
I can understand not having 2FA turned on by default, but a bare minimum for this kind of service would be to alert users when someone successfully logs in from a new device.