The later 700 phones had everything fixed to the base and the top part was then just a cover (much like the Western Electric 500). These earlier phones, however, just had a cover plate for the base with all the works fixed inside the top part of the casing.
And for all you sharp-eyed viewers, can you spot the one item here which is not original G.P.O. issue?
Like many of the old G.P.O. telephone sets, this phone was made by Standard Telephones in North London (my mother worked there for a while):
Electrically, the 332 set predates the use of regulators, so the internal circuitry is quite simple. Here's the schematic from inside the base plate: