Most of the creatures listed at the back of the PHB are in the SRD under the "Animals" section. Most of those that aren't (Imp, Pseudodragon, Quasit, Skeleton, Sphinx of Wonder, Sprite, Zombie) are in the "Monsters" section.
The only ones that appear to be missing entirely are the Octopus and the Slaad Tadpole. I can kind of understand the Slaad not being in the SRD, but the Octopus seems like a strange one to miss. (The SRD has a lot more animals than the PHB, and seems to otherwise mirror the MM for that section.)
Since the SRD should be using the Errata'd form of the creatures (ie: from the Monster Manual), then that should be almost entirely sufficient for reference purposes without needing to buy the Monster Manual.
Note that in a quick check of a couple creatures, I couldn't find any differences between the PHB and the MM, so I'm not actually sure what changes are supposed to be expected. In that regard, the Errata still fails.