As others correctly pointed out, PBXes in general, call logging included, are a proprietary hell. They've managed to avoid standardization for so many years, every manufacturer fighting tooth and nail to be able to sell their proprietary hardware to old clients (Customer Retention 101).
That said tho, I think you may be better off if you get some terminology straight and then start a more precise Google searching armed with proper terms.
PBX logs can be called CDR (call detail record) or SMDR (station message detail recording). As an Avaya guy I used to deal with formats such as
59 Character Expanded INT ISDN LSU .. and the most fun of all: .. Unformatted
This is by no means an exhaustive list, you will *definitely* encounter more, and I would presume that different manufacturers may be calling the very same format by different names, too (just to stay on the safe proprietary side - see Customer Retention 101)
I sort of vaguely remember that some of the formats have their own Wikipedia entries, so not all is lost here. You may be able to find enough useful info to start your project from just some free internet resources.
The way to extract that data from the PBX can range from catching output of an RS232 port to TCP or UDP data stream, to opening a certain file from a certain location on a PC that's connected to PBX in a magical proprietary way :) I am certainly not aware of one standard API (no standards allowed here - see Customer Retention 101) for log extraction.
------------------------------------- Best Regards, Dmitri Abaimov, RCDD
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