Thanks, I'll see what I can find, but plenty of 2g and 3g rugged phones are unusable now because of network shutdowns even though the phone hardware is still perfectly good. I have several non-rugged phones in similar straits. I'm told that 4g is now gradually getting displaced by 5g, though I expect it will keep working for a while. That and replacement battery availability seem like limiting factors. Also, from sad experience, the micro USB charge port has finite lifetime so I wonder what it will take to repair it.
The DuraXE does look like a good phone though it has imho non-dumbphone features like wifi. I guess I better check its network coverage and will look into it. According to PC Mag it runs Android 5.1 under the covers, which is a little bit scary to me.
A Baofeng ham walkie talkie is about as rugged as a typical "rugged" phone and costs around $25 so I don't see why there's no phone in roughly the same format. Until the 2g shutdown you could buy 2g phone modules for a few USD, that had some analog audio wires and some control lines and a power wire, so you could make your own phone around it pretty simply. Sparkfun had a product that was one of those built into a vintage rotary phone. I don't think they have those modules for 4g or 5g but I should look again, I guess.
Added: aha re 4g modules, this is $60+ but looks interesting, and makerfabs has some other neat stuff:
https://www.makerfabs.com/maduino-zero-4g-lte-sim7600.html