Not sure this is a fix yet but seems to be working
In Settings->Apps->Installed Apps->Phone Link, click the menu to the right and select advanced settings. There is an option for background apps permissions. You probably have it set on power optimized which would explain why it fires up when the screen sleeps. I think changing this to never will definitely solve the problem but may not be best choice if you want the app to be active while minimized. I am also testing the always option so it does run in the background always, but not triggered by the screen sleeping. In this mode, the CPU may be lower and more consistent. Hope this helps.