Previously I tested out the electron gun and I didn’t see a beam on the phosphor. I wanted to rule out the possibility that there WAS a beam, but it wasn’t hitting the phosphor screen. By moving the screen closer I can see the beam no matter where it is pointed.
So I designed and printed this sweet phosphor holder:
I have a small piece of broken phosphor glass from the CRT. I used the excellent OpenSCAD polygon editor to make a form fitting mount:
In real life:
That was easy!