I can’t download my iPhone 8 phone book into my 2012 Grand Cherokee Uconnect.

Hey, there, owing to most ibooks are protected by DRM, even if you have transfered the files to your iphone 8, you may not read the books smoothly on the devices. You can try to share the Kindle account between the devices, or transfer via USB. you can also try to remove DRM from the book. Check out this guide. Can Share Kindle Books on Multiple Devices

According to How to read ibooks on PC, you can use ApowerMirror or EaseUS MobiMover to download ibooks from iPhone.
How to Read iBooks on PC

Turn iPhone Bluetooth On:First you want to make sure that Bluetooth is functioning on your iPhone. Click on the Settings icon from the iPhone desktop. From the settings screen click General to show the iPhone General Settings as displayed in the below image. Notice you can see if Bluetooth is on or off from this screen. General Settings screen you can click on Bluetooth to configure the Bluetooth settings. On the Bluetooth screen shown below click to the left of Off to turn Bluetooth On.

1. Begin Uconnect Setup:Now that Bluetooth is operational on the iPhone you can start the Uconnect process. Click the Uconnect button on the rear view mirror to begin. The voice from the Uconnect system will ask you to verbally select one of the options from the menu. Once Uconnect asks for your input say "Setup" to begin the process of syncing the iPhone.
2. Start Phone Pairing:Once you say setup in the above step the Uconnect system will list numerous options available from the setup menu. One of these options is "Phone Pairing" so when the Uconnect system asks for the choices from the setup menu say "Phone Pairing".
3. Pair a Phone:In the Phone Pairing menu you can modify current entries or begin pairing a new phone. After Uconnect lists all of the choices you should say "Pair a Phone" to begin the process of pairing the iPhone.
4. Uconnect Pin Code:The first step in pairing a phone is setting the Bluetooth Pin Code that authorizes that phone to pair with the Uconnect system. When asked for the Pin Code say any four digit combination such as "1 - 2 - 3 - 4". Uconnect will repeat back the Pin Code so you can verify it has recorded properly.
5. Connect iPhone To Uconnect:After you have set the Pin Code for the Uconnect system you need to view the iPhone's Bluetooth Settings screen which you can get to following the steps in Step 1 above. Before the Uconnect system shows up in Bluetooth the Bluetooth Settings screen will look similar to the below where you may have other Bluetooth devices showing or not.After a couple seconds the Uconnect system will display as "Hands Free" as shown in the below image. Notice it states that it is not yet paired,,,,,
6. Click on the Hands Free device showing in the Bluetooth devices list above. This will open a new screen as shown in the below image that prompts you for the Pin Code you specified in Step 5.
   
   Enter the Pin Code and then click the Connect button in the top right corner of the above window. This will pair the iPhone with Uconnect and take you back to the Bluetooth devices screen where the Uconnect Hands Free device will now show Connected as shown in the below image.
   
   After the device is connected you will be prompted by the Uconnect voice again so proceed to the below steps.
7. Phone Name & Priority: After connecting the iPhone you will then name the phone and set a priority between one and seven. Name the phone anything you would like and if this is your primary phone set the priority to one so this phone always connects at a higher priority than any other phone.
8. Verify & Test:Now have a friend dial your cell phone while you are in your car to see if the music volume lowers and the Uconnect voice tells you there is an incoming call from a certain number. To make calls you can press the Uconnect button and follow the voice prompts.
The Uconnect system is a great way to safely use your cell phone in the car.