Only available in Europe apparently, I was sure I saw this first on the core, but a search did not find it.

One of the draws for me is the replaceable battery. On a long trip, replacing the battery would be golden.

I think its a bit too big, the camera gets a bit of a slating (Probably OK for me) and I tend to enjoy waterproof phones, which will be difficult being modular.

https://www.fairphone.com/en/

I've been drooling over the Fairphone for awhile.  Unfortunately we can't get it in the US.

The nearest thing in the US is the Teracube 2e.  The Teracube comes with a 4 year warranty and is designed specifically to be repairable: replace battery and screen, but I'm not sure how modular it is.  It uses a lot of recycled plastics, soy ink, minimal carbon footprint, etc.  Teracube comes in 2 flavors.

1. Standard. This has regular Android on it. So Google will know when you go to the loo.
https://myteracube.com/pages/teracube-2e

2. /e/ Foundation version.  Same brand new Teracube 2e, full 4 year warranty, but the completely de-Googled /e/ operating system is installed at the factory.  In fact this is the only official /e/ phone available in the US.  Works on T-Mobile and ATT networks only.
https://esolutions.shop/shop/murena-teracube-2e-emerald-na/

It appears both versions are available also in CA, EU, UK.

I like the replaceable battery and the price.