What is wrong with this code

[vgdd]

for (int i=0; i<= phrase.size(); ++i)
{
cout <<"Character at position"is": <<phrase[i] << endl;
}

[lastchance]

cout <<"Character at position"is": <<phrase[i] << endl;

At a rough guess, you meant to write
cout << "Character at position " << i << " is " << phrase[i] << endl;

[Peter87]

The size of the container is not a valid index so you need to use < instead of <=.

for (int i = 0; i < phrase.size(); ++i)