Perhaps you are talking about the turn by turn voice prompts from the iphone through the Spider's speakers?
If that is the case, there are two ways to get voice, but both depend on Bluetooth being paired first of all.
1st method: If you are using the audio source of your Spider's radio, Pandora, USB or Sirius while in Apple Maps and after a destination has been entered, on the iPhone scroll up from the bottom menu and click voice, then ensure HFP prompts are enabled. Apple Maps will interrupt those sources as if a phone call was coming through, so the clarity will not be as great as HiFi Bluetooth below, and there may be a bit of lag.
2nd method: If you are playing music from your iPhone, and thus have selected its paired Bluetooth as your Spider's audio source, there should not be anything else to do. This is how I use Apple maps most of the time.
If you rather not have any audio playing, just choose your Spider audio source to be your iPhone's paired Bluetooth anyway, play one song if it does not immediately activate, then cancel the song.