So I used to use the “Armada FB” app on my phone, but it’s apparently not being updated. What programs are you guys using?

My favourite: Armada Fleets Designer

http://www.dmborque.eu/

You can download an .apk to install it if you're using an Android device. If not, you can register and save fleets.

The guy behind it keeps it updated often.

I use Armada Warlords - it's not an app, though. . .

There are four major ones that are being actively maintained AFAIK.

Armada Fleets Designer has the best UI IMO, but only in the Android native app. It does have a webapp as well, I just don't like it as well as some of the other web-based ones. A small payment gets you cloud storage for all your fleets.
https://swm-dmb.blogspot.com/2018/10/welcome-to-x-wing-squads-designer.html

Armada Warlords is the fastest to update generally, and has pretty big userbase. I find their UI clunky personally, though they do have a "compressed" one in beta that looks promising. It's also ad-supported, which is a little offputting to me; but I'm sure it offsets costs, so... *shrug*
https://armadawarlords.hivelabs.solutions/

Kingston's is nice, I like his UI the best of all the webapps, and updates relatively quickly as well, but in my experience is prone to enough "little" errors to erode my trust in the site a bit. Similar payment for storage model to AFD, though I believe you have to pay a small one-time payment to save at all.
https://armada.ryankingston.com/

Armada Flagship is the new kid on the block, though it's been around a year or two at this point. I was a bit cool on it early on, but I've been fiddling with it more lately and it's pretty good these days. Also has a lot of unique and fun analytics stuff in there that makes it worth playing with. Fully free AFAIK.
https://flagship.barronsoftware.com/

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I've also heard talk of people picking up maintenance of ArmadaFB and the Armada BattleScribe module, but it's only rumor at this point. And Fab's is the OG, and still live, but hasn't been updated since the SSD.

Edit to fix formatting. That was weird.

It may still get updated. I use it too, and I think it took 2-3 months to get updated after Wave 7. I don't know if the developer isn't very engaged in Armada anymore, or if it just has to do with the slow pace of development in the Apple store sandbox.

Flagship is also a progressive web app, so if you visit it on a phone you should get prompted to "install" it on your phone to get a native-ish experience.

The folks behind this great Legion builder said they are making one for Armada. That's all I know.

https://legionhq.thefifthtrooper.com/