Getting a true open-source only OS running on a phone? Android?

I've read a lot, and heard both sides, but still slightly in the cloud when it comes to android. Android is a open source OS, but when I buy a phone, it comes preloaded with google services and apps that are clearly not open-source, and are integrated at such a level a cannot remove them. Only "disable" them. If android is truly open source, can I compile my own image and flash it to my phone so that I am running a 100% open-source code OS on a mobile platform? (I'm thinking in the mindset of Debian, where all code is open source and available to the end user)