Making a phone would be a fantastic end goal, but I think support for a privacy focused EU based phone manufacturer might be easier, faster and cheaper.
Would the Shiftphone 8 or the Farephone 6 be a suitable replacement?
Would really love one these phones to be the official GOS phone :) but I have no idea if these would meet the security requirements, I did see that CalyxOS have upcoming support for the ShiftPhone 8 and already support the Farephone 5.
Privacy and security are 1 part of the puzzle, but reliable and repairable are part of my equation for hardware choice these days, I already made the decision when I shifted to GOS and a Pixel, that I will never buy another iPhone again, and now that repairable phones are a thing once again, I will never buy a phone without a quick removable battery either, so I would really love to see GOS move to one of these types phones.