The phonology that they share is not really that simple. There are too
many fricatives, for example. Not to mention consonant clusters, which
both have in abundance.
It is simpler than that of natural languages like Danish, French, Hindi, Russian, Arabic, Chinese, Japanese, or even English. Apparent evidences of such simplicity, at least in Lojban, are:
1) the fact that markings like diacritics, which are prevalent in the description of natural languages' multiplex sounds, are basically non-existent (except when telling that some particular sounds with such markings are permissible);
2) there are no coarticulation and double articulation which are the manifold/complex versions of single/simple articulation;
3) the vowels are straightforward in a way that distinction between the rounded and its unrounded counterpart isn't prescriptive (
i.e. roundness is not phonemic in Lojban, unlike e.g. French, where you can't mingle them up).
That's why I've come to think the phonology of Lojban is relatively simple.
Obviously I'm not as experienced a speaker of Lojban as you are; so I'd like to learn more about your argument: In what aspect can the fricatives and consonant clusters in Lojban be said to be abundant?
(If fricatives look to be large in number, I think that has to do with the fact that there are more variations of human fricative sound than, say, nasal or approximant, in the first place. Indeed, it is fricatives which are the largest in the IPA consonant chart, approximating to the number of vowels.)
> I'm not completely familiar with Esperanto either, but I'm convinced that
> Lojban is linguistically more open than Esperanto can ever be.
Phonologically, they are very similar. In other aspects, such as grammar
and vocabulary, they are quite different. "Linguistically open", I don't know.