Party chat killed mic sadly. It was a great way to make friends back in the original Xbox and early 360 days. I kind of miss it. That said, I only use the keyboard if it's an option. FYI, you can use your voice to type in PSO2 or use the Xbox phone app. The X1 virtual keyboard does voice-to-text.
Its kind of clunky though it, doesn't work very well. I'd rather just pickup a $10 keyboard from Amazon, its much easier.