Some companies like to roll out just an app with no desktop equivalent. An Android phone with the SIM taken out is also one of the few ways to create a new Google account without disclosing your phone number nowadays.

My first instinct is to recommend a recent Pixel with GrapheneOS:

• Make sure to buy a factory-unlocked model so that it’s not locked down to the stock OS. Preferably also gently-used second-hand so no money goes directly to Google.
• Of the options, GrapheneOS gives you the most compatibility, security, and updates.
• Installing GrapheneOS can be intimidating at first, but it’s pretty hard to mess up if you install through a Chromium-based browser.

I’ve also used CalyxOS and it’s a solid option that supports a few models outside of Pixels. But if you end up needing Google Play Services, you’ll be stuck with its replacement microG, while GrapheneOS offers sandboxed full-fat Google Play Services. While still secure, it’s not the hardline security of GrapheneOS.

I have no experience with FairPhone or Linux phones. Fairphones’ main attractions are the easily replaceable battery and microSD slot. Linux phones are still too cumbersome for the regular user to daily drive.

EDIT: see also this table comparing privacy-focused options https://threecats.com.au/comparison-of-custom-alternative-android-os-roms-grapheneos-divestos-calyxos-iodos-eos-lineageos-stock-android-aosp

In the US, AT&T, Verizon, and T-Mobile have an oligopoly over the cellular infrastructure. All of the other carriers (MVNO) just piggyback off the infrastructure of the big three. Traditional voice calls and SMS (“green bubble”) texts are unencrypted and logged, no matter the carrier. Carriers can also perform cell tower triangulation and track the IMEI, which is permanently associated with your phone, surviving even an OS reinstall.

One way you may try to avoid handing over identification at activation or payment for cell service is to buy a 1-year prepaid SIM with a prepaid gift card to a trusted friend’s or otherwise shared mailbox. Or buy a prepaid SIM at a brick-and-mortar store with cash and top off with refill cards thereafter.

Common vulnerabilities: Tracking by carrier, including cell tower triangulation, SMS, and call logs.

Non-smartphone specific vulnerabilities: Lack of security updates. However, the data to be exfiltrated from a non-smartphone is limited. If it’s only call logs and text messages, everything’s already compromised by virtue of the carrier. So the level of concern will vary with your threat model.

Smartphone-specific vulnerabilities: Tracking by apps, manufacturer, OS vendor, or just about anything that can take advantage of the smartphone’s computing power. More data to be exfiltrated if it falls to a security vulnerability.

Smartphone-specific advantages: Can be run Wi-Fi only to avoid tracking by carrier.

Can relate. I have a phone with stock Android and a removable battery for anything won’t or I’d rather not have on my primary GrapheneOS phone. I only ever plug in the battery as needed and when I’m settled at the safety of my desk.

That’s quite appalling. Might try out LeOS, also curious why it isn’t brought up more often. Perhaps because the color scheme screams “I paid for all 16’777’216 colors so I’m gonna use them all!”? Not a dealbreaker for me, but if you have used it, is there an option for less colorful icons?

Awesome, adding to my current arsenal of alternative clients alongside FreeTube and NewPipe. One less chance for YouTube to force me onto their webpage.