>I thought there was a robust android emulator for linux such that I could run android apps - and call an Uber or whatever - from desktop linux ...

There are some but not really great and it will become impossible very soon with remote attestation and play integrity. Already Uber is one of the few apps that have the hardware attestation keys for grapheneos manually added.

In my experience, Waydroid works very well actually. The question is whether it wouldn't just be simpler and better to use AOSP (or Graphene) as the OS for these phones. In principle, a "Linux phone" sounds great, until you realize that there are close to zero Linux programs that are actually usable on a small touch display. The Android project already has done the hard work of adapting Linux to mobile devices and FOSS apps are plentiful and polished. The problem with the common variety of Android phones is control by Google, not the underlying tech.