Cisco SPA504G (older phone) not listed and not sure what the provisioning should be?

I am fairly certain that that phone will not be supported at all by Zoom. Do you have a lot of them you want to provision? There is a small chance you can get support to allow them as generic devices, but I am pretty sure they don’t meet the specifications required. 

We are using old Poly IP335 phones, while at end of life, still supported for at least another year. Basically hoping that the people still using desk phones can be convinced to move to the Zoom app.

If the phones stop working at some point (no hard date for them to no longer function with Zoom), we'll get Yealink phones as needed for the people refusing to use the app.