This is the 815th most frequent Ukrainian word.
мама
Mother.
Here, 'мама' (/mama/) is used as a direct reference to one's mother, fulfilling the subject role.
Мама любить пекти пироги.
Mom loves baking pies.
In this case, 'мамою' (/mamoyu/) is the instrumental case of 'мама', indicating the means of action (in conversation).
Я розмовляв зі своєю мамою сьогодні вранці.
I spoke with my mom this morning.
Here, 'мама' is again the subject, but used in the context of temporality and planning.