If your old phone was also eSIM compatible, you can just download the eSIM from your carrier like you would if you moved to any other phone.
If we disregard the fact that many older but still usable phones don’t support e-sim (which was the original point), what do you mean ”just” download the e-sim?
At least in my country, getting an e-sim is a pretty involved process which requires secure authentication, and specifically in my case that authentication would be gone with the now-broken phone if one didn’t have the foresight to have a backup (which many people do not).
If you have a physical sim, you can move it to almost any (unlocked) mobile phone in existence (at least in Europe) and at most you’ll need the PIN/PUK.
Of course, this goes the other way as well if you drop your phone in the ocean for example, provided you have alternate authentication and a compatible phone, e-sim will have you up and running again much faster.
Password to Flex itself is in my 1password db. If that gets compromised I'd have way bigger problems than cloned phone number.
Carriers are the real problem here, not letting you easily switch between a physical SIM and an eSIM in case that happens. Some do, but you usually have to call up, there are delays, etc. Ideally it would be an easy switch in their web admin panel.
Now you might retort aha! See! In a very narrow set of circumstances.. let me cut you off, look, you're going to need to remember to bring a paperclip or sim tool to do it the old fashioned way anyhow. So you're remembering something. If you're an amnesic lost in the woods you got bigger problems.
Besides, those are 2 grams of weight savings in my ultra light backpacking setup!
My old phone is still logged in to Apple, still works, still holds a charge. I'd like some eSIM system that was as convenient as "phone dies, pull SIM, put in old phone, boot".