Is “ekphrastic” poetry composed from the Greek words ek (out) and phrazein (tell, declare, pronounce), ekphrasis, originally meant "telling in full"?
The etymologies I was able to find are consistent with the one posed in the question, and so "ekphrasis" refers to the pointing out or explaining of something in detail.
I've pulled from a few sources here.
From the website wikitonary, the etymology (or development of the word) of "ekphrasis" is:
ἔκφρασις (ékphrasis, “description”), from ἐκφράζω (ekphrázō, “I describe”), from ἐκ (ek, “out, ex-”) + φράζω (phrázō, “I explain, point out”).
From wikipedia, the etymology is shown as:
The word comes from the Greek ek and φράσις phrásis, 'out' and 'speak' respectively, and the verb ἐκφράζειν ekphrázein, "to proclaim or call an inanimate object by name".
And so yes, the etymologies here fit with the etymology in the original question, in that we're talking about poetry that was originally designed to talk about something in full.
Ekphrastic poetry in modern times refers to poetry that is written about a piece of art (the wikipedia has an example of ekphrastic poetry written about the Mona Lisa). But in ancient times it referred to poetry that was filled with vivid (and one could say other words such as "painstaking" or even "mind-numbing") detail. For instance, in the link below, there is a reference to the Iliad, a Greek epic poem, that spends 150 lines on the description of the hero Achilles' shield!