The 1.100VZ software update was applied to my Kyocera DuraXV Extreme (E4810) on 07/21/2020. Since the update, the phone defaults to speakerphone when I answer a call. This occurs regardless of the state of the "Open to answer" call setting.
I've modified other settings, such as the programmable keys, to no avail.
Perhaps the next software update should include an option to completely disable the speakerphone.