Who am I speaking with? or Who I am speaking with?

I'm puzzled. I realize that "Who am I speaking with?" is acceptable, but I don't think it's grammatical.
Would you say, "I was speaking with he yesterday." ?

The preposition "with" takes the objective case." "Whom did you come with?"
"Did you come with him?" Not, "Did you come with he?"

(It's okay to ask "Who did you come with?")

Addi

I agree with much of what Avangi says, but may I start from the beginning?

These are the generally accepted options, at two levels of formality:

Who am I speaking with? -- less formal, very common

With whom am I speaking? -- very formal, but receptionists are sometimes enjoined to use it.

It is generally considered 'incorrect' or at least badly mi

may i know to whom i am speaking?(correct)

may i know to whom am i speaking?(incorrect)

before getting to that i make it clear of this basic rule

"wh" question+helping verb+subject+main verb {always}

what are you doing

where do you play badminton

but in this sentence{may i know to whom i am speaking?}

whom act as "relative" pronoun and not as "questio

Never end a sentence with a pronoun.

Is it ok to answer a phone with “who am I speaking with today?” Or must it be “To whom am I speaking with today?”