my wife often wraps up phone conversations with something that i wasn't getting for a long while, "thaa ngan".

turns out, that means "in that case", ถ้างั้น, thaa ngan

I have heard that same phrase but never quite worked it out other than the first word 'if'. Thanx. ..

Coincidentally, when I first moved here and would hear thais end phone conversations often I would hear what sounded like "Canada..." just before they hung up. I worked out on my own they ALL couldn't be talking to Canadians and that 'Canada' wasn't a secret code word for something else.

I learned much later it was the phrase; แค่นี้นะ (khaaeF neeH naH). My ears which were not used to hearing thai interpreted it to my brain in english as; Ca-na-da.

Oh well, live and learn.

my wife often wraps up phone conversations with something that i wasn't getting for a long while, "thaa ngan".

turns out, that means "in that case", ถ้างั้น, thaa ngan

I've never heard it as a phone conversation ender although maybe that could be a matter of personal usage or a dialect I am not familiar with? In my experience, ถ้างั้น usually starts a sentence, i.e. 'If that's the case... (then) etc.).

แค่นี้นะ (khaaeF neeH naH) and แค่นี่ก่อนนะ (khaaeF niiF kawnL naH) seem to be the most common ones in my experience.