iPhone automatically switches to a cell network

My iPhone 12 Pro works great everywhere but my house. We're at the bottom of a hill surrounded by trees and receive a weak, inconsistent cell signal. However, I do have great wifi through my cable provider, Comcast. My phone is set for wifi calling, but whenever it senses a sufficient cell signal (1 or 2 bars), it automatically switches over to the cell network. Then, the signal inevitably fades and the call deteriorates and drops.

How can I make my phone stick with the strong wifi calling signal instead of migrating to the weak cell signal it detects? Are there certain phones that will not do this? Would a femtocell help solve the problem? Any input would be much appreciated.