etathrax What constitutes a reasonable solution depends on a number of details you haven't shared yet, but I can share some of what I've learned, regardless, since I'm a couple steps ahead of you.
At the most convenient, "high" level where you take a few basic steps to noticeably improve your privacy (and even security) over Apple, you could use GOS with a Pixel 8 or 8 Pro, set up a VPN, and optionally an on-device firewall such as Rethink DNS. From there you can decide whether or not to use Voice-over-Wifi (which can bypass a VPN). Your carrier can still track your location due to using cellular telemetry, but they would have a very hard time probing your data-based traffic if you use a reputable VPN with the right settings.
Once Rethink v055b comes out, it's supposed to allow for a form of tunneling that allows you to hide DNS traffic from your (IP-based) VPN and vice versa. I'm not aware if another app could allow for that robust of privacy with data traffic shared with those parties.
Whenever you don't want your location tracked, set airplane mode on plus Location, WiFi, and Bluetooth off. You still need to consider apps you want to install that want sensor permissions, since they could theoretically record sensor data with timestamps and compare to other devices around you, but that's up to you how serious you want to get with it.
Then you could rely on sandboxed Google Play for any apps that need Google frameworks. But keep in mind if you're using a non-anonymous account, there could be apps you install which share data with Google through ICP.
And in fact any apps can talk to each other if they both "collude", which bring us to another "level" down as it were: to sandbox some apps via user profiles. The most common version of this is to sandbox Google Play and apps reliant on that into their own profile.
Just keep in mind that user profiles immediately add more complexity and inconvenience for a benefit that varies from very little to a lot depending on your setup.
It's important to think about user profiles as separate devices. For example, lets say you keep non-anonymous Google apps - such as work accounts - isolated on their own profile. If you use Zoom, will that be on the same profile? Zoom could theoretically share data via Google Play or to another app via ICP (they've gotten in trouble for privacy issues on multiple occasions), but if you have it on a separate profile, if someone sends a Zoom link to your work gmail now you need to find a way to copy and paste the link between profiles. Or what happens when you're listening to music and want to switch profiles?
Finally, given how much you value your number, I'd argue the next level "down" is to port your number to a privacy-friendly VoIP provider and get a data-only prepaid plan you pay for in cash. The main benefit of that is you keep your phone records private, but in the case of paying in cash, the carrier could still potentially know that you are on a Pixel 8/Pro that isn't stock that's using data somewhere within a few block radius. Even in a moderately dense area, that could still be pinpointed to you personally, but them sometimes knowing a specific person owns a weird Pixel 8 that uses certain amounts of data at certain times is enough privacy and anonymity for most folks. Especially when their knowledge is hypothetical.