There are so many phones to choose from theoretically, yet none of them meet 3 basic demands I have:
- under 5.2” inch form factor
- more than 3G of ram
it’s crazy. It’s like all manufacturers met somewhere and decided: let’s all make big fragile phones
Give us precise dimensions, not just screen size.
Glass back shouldn’t be a problem if you use a good case. The screen will be the weaker point.
It makes absolutely zero sense to have these thin lightweight phones and then add a thick heavy case around it 
I have have a glass back phone without case. Dropped once and cracked. Slippery as hell too! But I flat out refuse to use a case. (disclaimer: it’s my workphone, so I tend to not care so much)
The current phone I have has 70x135mm dimensions and 5” screen.
I would accept up to 75x145 but not more.
Closest phone I found that I might like is the Blackview BV6600 Pro, because it has a big battery and a thermal cam… but it’s also huge, 80x160 
Well, let’s go with the Google Pixel 4A then 
Ticks off all the criteria: size, plastic back, more than 3GB of RAM.
That is a good one.
My wife and I both have a 4A 5G and it’s been fine for us. Battery life is 2 to 4 days depending on usage of course.
There are some thin cases with protruding edges.
The glass back is usually cheap to replace (unless it’s an iPhone). The screen on the other hand is quite expensive. Smartphones are not made to be dropped. The screen can break at any time.
I don’t have the Pixel 4a, but my wife has a Pixel 4 and I have the Pixel 5 and they are great phones.
Pixel 5 is not too much bigger than 4 and has 8G memory.
How is the battery?
I see it has one of those useless high density screens that probably draws a lot of battery.
A 1080p screen is now useless?
"- under 5.2” inch form factor"
That's kinda small these days.
I have a budget phone to recommend, but it's way too big for you.
resolution is too high for the physical size. you don’t notice pixels after 720p.
so it’s just wasted battery life…
my ideal phone would be iphone SE 2016, but with Android and more memory and better battery
Whats your current phone?
Why are those the requirements? Wireless charging make the backs glass. I have an iPhone SE 2020. I hate the form factor. I just buy the next iPhone but I will try android next once I can relay iMessage to it. I like the smaller phones but I got used to the larger ones. Smaller ones tend to not break though.
The market demands it so they make it. I would suggest the S10 lite. Got an SD card still, good roms, larger than you want but pretty small in my hands. Budget androids are really good. The S7 fits your needs and is probably super cheap right now.
The Pixel 5 actually has a great battery. I can easily go for a few days. They oversized the battery because they wanted people to buy it for its ability to wirelessly charge other phones. I never use that feature, its just a gimmick to me. But I love the battery life. I don’t know what you mean by useless high density screens, I’m getting older and my eyesight is getting worse. The text on the screen is really crisp and easy for me to read. My mother in law also has the Pixel 5 and can read the screen just fine.
Something I tried a few beers ago was using Duplicolor Customwrap to create a very thin, grippy case for a cell phone. 6 layers of the stuff made for a perfect grip.
thank you, kat, for starting this thread.
i, too, am looking for a THIN and SMALL phone.
please post some phones that pass the thin AND small test.
I suggest looking through the gsmarena database: Phone Finder - search for a phone by feature - GSMArena.com?
Your options drop drastically when looking for non-glass backs, small size, and headphone jacks.
Phones are the single most abundant type of electronics you can buy today. If you cant find what you are looking for, it probably does not exist.