It can/does handle long phrases but there are some things to watch out for, particularly with a phrase as long as the one you show. First, watch out for pauses that trigger a stop in the speech processing (particularly at 'Good day'). Speech processing processes one phrase at a time so if it is split into 2, then each one processes independently. This leads into the second issue - FoxVox works by a command word followed by special key words. In the default library the phrase must start with "Ground" to activate the Ground command group, then include the word taxi (and not include "back" or "ramp"). From your example, you would have to add "Gunsan" to the ground command group to be successful or make "Ground" a wildcard by adding an asterisk "*" behind it (meaning it doesn't have to be the first word spoken and can come anywhere in the phrase). Making it a wildcard would have negative repercussions however as "Ground" is used in other key phrases for wingman, i.e. "Two, datalink ground target" or "Two, weapons free air to ground". These commands wouldn't be executed properly because the ATC Ground command group would be activated instead of the Wingman group due to the wildcard and its earlier position in the list. I may do a revision to prioritize keywords found at the beginning of the phrase over wildcards first, but currently that's not how it works.
So from this, you need to be sure that the processed phrase is found. I experimented with your wording a bit and found that adding both "Taxi*" and "Departure*" as wildcards to the ATC Ground command group seemed to work best. I also added "Departure" as an optional word on the Request Taxi command and as a blocked word to the Request Taxi Back to Ramp command to help prevent an accidental misfire. Doing this seemed to give the best results regardless of pauses being present or not. I just had to focus on making sure "Taxi" and/or "Departure" was understood properly. Also, remember when testing and troubleshooting, be sure to enable the enhanced log to see what is being tracked as you speak. I also think I can possibly make some enhancements with really long phrases that might help in the underlying engine...I'll experiment more for the next update.
I need to see about opening a channel on discord - good suggestion. There's not many people using FoxVox currently, but who knows, might be more in the future.