Before Let's Encrypt I had created my own certificate authority certificate, which I signed my http, xmpp, and mail-certificates with.
To stop my phone from complaining about the dangerous, unsafe, unhealthy, and non-glutenfree certificates, I installed my ca-cert on the phone.
For some reason I cannot fathom, Android mandates that I then must have a lock screen with a pattern/password/something, and the phone also insists on warning me when it boots that my every network move can be monitored.
So, a nice bonus of switching to Let's Encrypt certificates is that I can de-install the home made ca-cert from my phone, and get rid of the annoying pattern-lock screen! ⊗