Is "all" plural?

Gramatically the word itself is not plural; it will precede a plural noun, but the word itself is not plural. The word 'all' can not carry a tense or be possesive, so the answer to your question is no.

The word all is not plural.

All Plural

That is a good question. I think it is plural. You would say "all phones must be off."

all is not plural it would be correct to say all phones must be shut off

All implies plural. "All phones must be off" = "They" must be off. If you can replace a noun clause with "they", it's plural.

All phones must be off. If you wanted to say one, you would say the phone must be off. All implies there is more than one.

For the best answers, search on this site https://shorturl.im/awyQw

It's just babby, as in "They are taking the three babby back to New York too lady to rest."

all phones must be off. all is not always associated with plural though.... all of that, all of this, all of the other, all of me, her, his, it,

Your ear must tell you that the second answer is not grammatically correct. "All" is not a noun, so it is neither singular or plural.

I say 'babbies'. When I'm feeling extra silly, I just use babby the way it is for plural.