Error when running phasmerge: too many files open

[jel4h]

I'm trying to run phasmerge and it's throwing the following error:

Traceback (most recent call last):
File "phasmerge.py", line 2704, in
File "phasmerge.py", line 2539, in main
File "phasmerge.py", line 1708, in PPResults
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/context.py", line 119, in Pool
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/pool.py", line 212, in init
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/pool.py", line 303, in _repopulate_pool
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/pool.py", line 326, in _repopulate_pool_static
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/process.py", line 121, in start
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/context.py", line 277, in _Popen
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/popen_fork.py", line 19, in init
File "/grid/sw/python/3.9.5/lib/python3.9/multiprocessing/popen_fork.py", line 65, in _launch
OSError: [Errno 24] Too many open files

I tried increasing the ulimit on my server, but I can't increase it beyond 4096.