SO anyone can trigger the code on my iphone easily?!
Yes. They simply have to use your Apple ID to try and access a service. The code is sent , but unless they have a trusted device of yours, they can't see it. Keep in mind, your Apple ID may very well be a known email address of yours.
"They" are, as 2SV provides for, blocked from accessing your account. Not from trying to, but from succeeding.
Annoying? Perhaps. But your account is not at risk just because of this.
I usually have to enter the password then the code, or recovery key then the code...
Yes, you do to move forward and access the service, but they can't.
They have neither the code or the recovery key. If they did, you would not be able to access your account right now, as "they" would have control.