Thanks to the great work by @gleonard3 have found this prints easily.

Have printed at from 0.2mmm layers to 0.08 and both have worked out great - both in Elegoo PLA

Printed at 15% infill and has worked out well for strength and ability to get on and off of phone.

I printed the plate at 5% infill as strength not required for its use.

For the transparent cover I cut around the plate print of a unused CD sleeve that was laying around - could use many different scraps of something transparent that you find laying around.

Allows for easy swapping of the Instax - just remove the phone cover and then the plate can easily come out its not held tightly.

(Please excuse my dusty printer lid…..)