Put potatoes in the bowl of a slow cooker. Pour the broth over the potatoes. Place the garlic and butter on top. Cover and cook on high for 3-4 hours, or on low for 6-8 hours, or until the potatoes are soft.
Use a potato masher, ricer, or electric mixer to mash the potatoes to your desired consistency. If you use a mixer, make sure you keep the mixer in the bowl or you will have a mess. Also, don't over mix the potatoes or you will end up with glue.
Stir in the cream cheese, milk, and heavy cream. Stir until well combined and smooth. Season with salt and black pepper and stir again. Transfer to a serving bowl and garnish with chives, if using. You can add an extra pat of butter on top, if desired. Serve warm.
Note-you might need a little extra milk depending on how thin/creamy you like your potatoes.