No module named '_phash' while running python verify.py

I followed setup instructions:
clone github repo, pip install -r requirements.txt

python verify.py wavs-test.txt phones-test.txt data.idx caused error:

:~/projects/vosk$ python verify.py wavs-test.txt phones-test.txt data.idx
Traceback (most recent call last):
File "/home/e.chernousov@avi.lc/projects/vosk/phash.py", line 14, in swig_import_helper
return importlib.import_module(mname)
File "/usr/local/lib/python3.7/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "", line 1006, in _gcd_import
File "", line 983, in _find_and_load
File "", line 965, in _find_and_load_unlocked
ModuleNotFoundError: No module named '_phash'

using python 3.7.0, ubuntu 18.04

Couldn't fild answers with google. What could be the problem?