Some phones have a more limited Application Storage partition, which ranges from around 1 to 3 GB depending on the phone. This is the only place apps can be installed, which obviously limits how many can be on the phone at once. This is how my Razr Maxx works, but I'm not sure if it's how the Razr M works. Some of the specs I've read say that the Internal Storage is "unified," so I assume it acts more like a tablet (which doesn't have a separate Application Storage partition).
Go to Settings/Apps/Downloaded, and look at the bottom--is there a storage meter that says "Application Storage," or does it just say "Internal Storage"?