Regardless of getting access to what is on your phone, the authorities can get access to your internet usage, messages, emails, phone log, phone calls, voicemails, etc.: anything that is transmitted to/from your phone through your ISP or phone company or that passes through or is stored on servers outside of your phone is potentially available for monitoring without anyone having to install anything on your phone.
"Po po" may or may not be a derogatory term for "police" but, to me, it sounds like something a two year old would say. You know, like "da da" and "ma ma" and "poo poo". I have no idea how a two-year-old's version of "police" became urban slang.