Are you worried that leaving the phone plugged into power will degrade the phone’s battery? The issue here is not so much charging time, since this is regulated by the phone and the battery won’t be charged for longer than necessary (otherwise it would be a dangerous product). Rather, the issue is the amount of time the battery spends at 100% charge while being baked by the heat from the phone’s circuitry.
If the battery will not be required for many weeks or months at a time, then removing it entirely while not in use might be the best option, just powering the device through the USB cable. (I assume that will be possible.)
Without removing the battery, the only option to prolong its life would be to limit how far it charges (say to 60 or 70% instead of 100%). With any luck this will be possible in software, but I don’t know whether it will or not. I believe this has been done on Android phones. Someone would need to write the software to get it to do that.
Here is a relevant (but inconclusive) thread about limiting battery charge in Librem laptops: Manually limiting battery charge