Q:

Why did my teacher mark down 一把 as a classifier for 手機?

My teacher detracted a few points for using 一把手機。It seems that 一台，一部, 一個 are better choices. However, I find many occurrences of 一把手機
Google search
Is it a dialectal phenomenon? Maybe in dialects where 把 and 部 sound similar？
Edit:
This source claims that 一把手機 occurs in 溫州方言

A:

To me, 部 is a formal classifier for 手机. 台 is usually used for a bigger machine, like computer & TV 一台电脑 & 一台电视.  一台手机 doesn't sound quite right to me. 
一把手机 is not used in practice for whatever reason. I guess it might be because 我要买一把手机 could mean you want to buy a handful of 手机s, implying several 手机s, not just one. 
Colloquially, sometimes I heard 一个手机 is being used. Like in the sentences: 我要买一个手机; 我想买个手机. 
Well, 我要买一部手机 sounds more formal and it's not as casual as 我要买一个手机 or 我想买个手机 in our daily communications. 
That's my observation from my neck of woods. Others from other regions may take this differently. 

A:

From Wiktionary:

把

Classifier for objects that can be held using handles or knobs, such as guns, chairs, brooms, umbrellas.
Classifier for handfuls of something, such as grains, soil.
Classifier for bundles or bunches.
Classifier for some abstract ideas, such as force, effort or age.
Classifier for something done with the hand.

I agree that「臺」or「部」sounds better (as a matter of perception; both are specifically used for machines/devices), because 手機 falls most appropriately into the last group, and sounds a bit vulgar (as if you're doing your cellphone).
I don't agree that「個」is better than「把」, though.

