on the part of ( or on my, their, etc. part)
used to ascribe responsibility for something to someone.
→ part
ON THE PART OF (OR ON MY, THEIR, ETC. PART)
Meaning of ON THE PART OF (OR ON MY, THEIR, ETC. PART) in English
Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004