Where is the code for the Bootloader stored in an Android phone? Where is the bootloader program on an Android phone stored ?
The boot-loader code is stored within the /boot partition. Majority of Android handsets uses the Qualcomm's Boot Loader, called LK (Little Kernel), barring Samsung, which uses their own form of boot-code.

LK has the following:


Variety of nand devices for bootup
USB driver to enable upgrading images over usb during development
Keypad driver to enable developers enter ‘fastboot’ mode for image upgrades
Display driver for debugging and splash screen
Enable Android recovery image and image upgrades


This applies to only, Qualcomm chipsets hence the exemption of Samsung based handsets

There is a website blog that cites this from source

The actual source code, if anyone is curious enough, can be found on CodeAurora site. This is known as CAF, in which a lot of Qualcomm specific code for kernels can be found in. 

As a side-note: Google releases source to AOSP, CAF, pulls from them, modifies it to make it fit within Qualcomm chipsets, then the Manufacturers pull those down and add their own bits, it is that for the reason there's, AOSP, CAF and CyanogenMod that are the main three flavours of Android.

The actual source code to the boot-loader can be found on CAF's git repository, and has not changed much, it can also be found in CyanogenMod's source, specifically in, /bootable/bootloader also.