I used to use resin/rpi-raspbian but this is unmaintained and still at stretch so doesn't have php 7.3 unless I start fiddling with /etc/apt/source.
There are also official docker php images as well as official php docker images (sic), I couldn't find out though how to chose which target architecture to build for.
arm32v6/alpine has php 7.2 only.
Do I still need to use qemu (Build Docker image for ARM architecture on Intel machine (Mac))? Totally confused now how to do this with reasonable efforts.