You can load multiple maps on Google before a trip. I loaded my 4 day trip from FL to MI that covered the entire route.
If you are hoping to use your older phone as a GPS only unit you can end the cellular service and use a local WiFi connection to load the Google Maps data to the phone and then it becomes a stand alone GPS for your travels. What you do lose is the traffic data which I find to be extremely valuable. The traffic data has saved me from sitting on the Interstate for hours twice now and it only required a minor detour through town to get to the next exit or a few exits down.