How does one "Press 1 for English" using voice on iPhone during call with phone system menu?
If the numbers are in your contacts.

You can Edit the contact by adding another number with some controls in.

i.e if you are always dialling : (888) 555 1212

And you need to wait 4 seconds and then enter a (1) for the selection.



You can Edit the contact and duplicate the number.

Then press the symbols button. 



which will give you two new buttons.

Pause and Wait.

Pressing the Pause button will add a "," at the end of the number.

AFAIK each "," will pause for 2 seconds. I am not sure about wait. Which I expect will be longer.



Once you have your pauses you can add the DTMF number as shown I have entered two "," to get 4 seconds and a (1) for the DTMF.



Repeat as needed for any other pauses and numbers and save. And dail.