This is the 13056th most frequent Russian word.
мамой
"Мамой" is the instrumental case of "мама," meaning "by/with (a) mom."
In this sentence, "мамой" is used in the instrumental case, indicating the person (mom) involved in the action of speaking by means of an instrument or method.
Я позавчера говорил с мамой по телефону.
The day before yesterday, I talked to mom on the phone.
Here, "мамой" is part of the instrumental construction used incorrectly; it should be "маме" to correct the sentence to proper grammar as "I always help mom," focusing on interactions centered around mom.
Дома я всегда помогаю мамой заботиться о растениях.
At home, I always help mom take care of the plants.
In this example, "мамой" again appears in the instrumental case, showing the relationship of mom to the situation or the people being satisfied.