Having to use my Phone to access my account.

Dear Sir or Madam
Since I came back from South Africa, nearly 3 years ago, every time I wish to view my emails I am asked to submit a code which is sent via my phone.
I did not ask for this service and how can I get this canceled. I am often in places where I am not allowed a mobile phone. How can my Yahoo account be reset so I am no longer at the mercy of my mobile phone to access my email account.
Yours faithfully P J McVey