My default security is access-locked, but I frequently edit posts to be public. However, I've found that it's impossible to change the security when editing on my phone. I am simply unable to get the button to acknowledge being pressed. Previously I was using a Samsung Galaxy Avant running Android 4.4.4 Kit Kat, currently it's a Huawei Nexus 6P running 8.1.0 Oreo. On both phones I use Firefox, currently version 65.0.1. I don't have any Firefox extensions installed on my phone.