Her body is pulled from the wreckage by a straggler cell of the Resistance, her armor smashed but intact enough to have kept her breathing in the vacuum of space for the day or so that she was adrift.

The ship doctors check her over and find that she's alive, but that she's been badly injured in the explosion, and is paralyzed from the waist down. They aren't quite sure what to do with her until they can get back in contact with the main group to ask, so after getting her stabilized they simply lock her up.

Phasma wakes up in a cell on a Resistance ship, stripped of her armor, aching like hell, and shackled to a cot.

And nobody onboard seems to speak a language that she understands.

+supplies are limited, and therefore aren't to be wasted on an enemy unless absolutely necessary, so she hardly ever gets pain meds
+her attempting to escape and finding out the hard way that she's paralyzed when she winds up on the floor
+she's super uncomfortable without her armor, but does her best to hide it
+Phasma assumes that she's being tortured for information because when the doctors occasionally come in to try and administer medication or see if they can fix her spine, they tie her down so she won't fight them, which only makes her fight harder
+she crosses paths with Finn again when she's about at her lowest point, and he shows mercy, which finally causes her to break down