Phone randomly slowing My phone is a Sony Xperia Z1s running lollipop, and I've noticed that this device loves to be very slow and choppy, even after a week after a clean install. The worst part, the slowing is inconsistent.  I have uninstalled Facebook, which seems to have helped, but not entirely. Are there any tips specific to my phone?
Does your phone have a cleaning system built in? If it does give this a try to see whether it makes a change. If not, maybe download an app such as Clean Master or something similar.

If worst comes to worst then you may have a virus. I recently had a problem with my computer graphics card where it suddenly became extremely slow. I found out later that I actually had a virus or malware installed without even knowing, which was affecting the graphics card's output (for whichever reason). Give malware-bytes or an anti-virus program of your choice to remove any possible issues you could have with the phone. If these don't work I'm afraid I can no longer help you :)